diff --git a/.github/workflows/main-s3.yaml b/.github/workflows/main-s3.yaml new file mode 100644 index 0000000..f92bd27 --- /dev/null +++ b/.github/workflows/main-s3.yaml @@ -0,0 +1,64 @@ +--- + +# Copyright 2023 Skyscanner Limited. + +# Licensed under the Apache License, Version 2.0 (the "License"); +# you may not use this file except in compliance with the License. +# You may obtain a copy of the License at + +# http://www.apache.org/licenses/LICENSE-2.0 + +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, +# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +# See the License for the specific language governing permissions and +# limitations under the License. + +# Tests for S3 Reusable Workflow +name: Main S3 + +on: + # Triggers the workflow on push or pull request events but only for the "main" branch + push: + branches: [ "main" ] + paths: + - '.github/workflows/reusable-s3.yaml' + - '.github/workflows/main-s3.yaml' + pull_request: + branches: [ "main" ] + paths: + - '.github/workflows/reusable-s3.yaml' + - '.github/workflows/main-s3.yaml' + + # Allows you to run this workflow manually from the Actions tab + workflow_dispatch: + +permissions: + contents: read + id-token: write + +jobs: + build: + runs-on: ubuntu-latest + steps: + - name: Make a file to upload + run: | + mkdir static + echo "i am a test file" > static/test.txt + - name: Put content into build time artifact + uses: actions/upload-artifact@v3 + with: + name: static-content + path: static + + reusable-s3-dry-run: + uses: ./.github/workflows/reusable-s3.yaml + needs: build + with: + dry-run: true + + reusable-s3: + uses: ./.github/workflows/reusable-s3.yaml + needs: + - build + - reusable-s3-dry-run diff --git a/.github/workflows/reusable-s3.yaml b/.github/workflows/reusable-s3.yaml new file mode 100644 index 0000000..0468c20 --- /dev/null +++ b/.github/workflows/reusable-s3.yaml @@ -0,0 +1,107 @@ +--- + +# Copyright 2023 Skyscanner Limited. + +# Licensed under the Apache License, Version 2.0 (the "License"); +# you may not use this file except in compliance with the License. +# You may obtain a copy of the License at + +# http://www.apache.org/licenses/LICENSE-2.0 + +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, +# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +# See the License for the specific language governing permissions and +# limitations under the License. + +# Reusable Workflow for S3 uploads +name: Upload to S3 + +on: + workflow_call: + inputs: + dry-run: + required: false + type: boolean + description: Displays the operations that would be performed without actually running them. + default: false + artifact-name: + required: false + type: string + description: Name of the artifact to upload. + default: static-content + +permissions: + contents: read + id-token: write + +env: + BUCKET: 'x' + ROLE_TO_ASSUME: 'arn:aws:iam::####:role/X' + REGION: 'x-x-#' + +jobs: + bucket-upload: + runs-on: ubuntu-latest + steps: + - uses: actions/github-script@v6 + id: prepare-aws-role-session-name + with: + # https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithWebIdentity.html + # RoleSessionName only permits [\w+=,.@-]* + script: return "GitHubActions," + context.repo.owner + "@" + context.repo.repo + result-encoding: string + + - name: Login AWS + uses: aws-actions/configure-aws-credentials@v2.2.0 + with: + role-to-assume: ${{ env.ROLE_TO_ASSUME }} + role-session-name: ${{ steps.prepare-aws-role-session-name.outputs.result }} + aws-region: ${{ env.REGION }} + mask-aws-account-id: 'no' + inline-session-policy: >- + { + "Version": "2012-10-17", + "Statement": [ + { + "Effect": "Allow", + "Action": [ + "s3:ListBucket" + ], + "Resource": [ + "arn:aws:s3:::${{ env.BUCKET }}" + ] + }, + { + "Effect": "Allow", + "Action": [ + "s3:GetObject", + "s3:GetObjectAcl", + "s3:GetObjectVersion", + "s3:PutObject", + "s3:PutObjectAcl" + ], + "Resource": [ + "arn:aws:s3:::${{ env.BUCKET }}/${{ github.repository }}/*" + ] + } + ] + } + + + - name: "Debug: sts get-caller-identity" + run: | + aws sts get-caller-identity --output table --color on + + - name: Download artifact + uses: actions/download-artifact@v3 + with: + name: ${{ inputs.artifact-name }} + path: /tmp/bucket-upload/ + + - name: List content to be uploaded + run: ls /tmp/bucket-upload/ + + - name: Upload to S3 bucket + run: | + aws s3 cp ${{ inputs.dry-run && '--dryrun' || '' }} --recursive /tmp/bucket-upload/ s3://${{ env.BUCKET }}/${{ github.repository }} diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md new file mode 100644 index 0000000..0e0931f --- /dev/null +++ b/CODE_OF_CONDUCT.md @@ -0,0 +1,76 @@ +# Contributor Covenant Code of Conduct + +## Our Pledge + +In the interest of fostering an open and welcoming environment, we as +contributors and maintainers pledge to make participation in our project and +our community a harassment-free experience for everyone, regardless of age, body +size, disability, ethnicity, sex characteristics, gender identity and expression, +level of experience, education, socio-economic status, nationality, personal +appearance, race, religion, or sexual identity and orientation. + +## Our Standards + +Examples of behaviour that contributes to creating a positive environment +include: + +* Using welcoming and inclusive language +* Being respectful of differing viewpoints and experiences +* Gracefully accepting constructive criticism +* Focusing on what is best for the community +* Showing empathy towards other community members + +Examples of unacceptable behaviour by participants include: + +* The use of sexualized language or imagery and sexual attention or + advances +* Trolling, insulting/derogatory comments, and personal or political attacks +* Public or private harassment +* Publishing others' private information, such as a physical or electronic + address, without explicit permission +* Other conduct which could reasonably be considered inappropriate in a + professional setting + +## Our Responsibilities + +Project maintainers are responsible for clarifying the standards of acceptable +behaviour and are expected to take appropriate and fair corrective action in +response to any instances of unacceptable behaviour. + +Project maintainers have the right and responsibility to remove, edit, or +reject comments, commits, code, wiki edits, issues, and other contributions +that are not aligned to this Code of Conduct, or to ban temporarily or +permanently any contributor for other behaviours that they deem inappropriate, +threatening, offensive, or harmful. + +## Scope + +This Code of Conduct applies within all project spaces, and it also applies when +an individual is representing the project or its community in public spaces. +Examples of representing a project or community include using an official +project e-mail address, posting via an official social media account, or acting +as an appointed representative at an online or offline event. Representation of +a project may be further defined and clarified by project maintainers. + +## Enforcement + +Instances of abusive, harassing, or otherwise unacceptable behaviour may be +reported by contacting the project team at open-source@skyscanner.net. All +complaints will be reviewed and investigated and will result in a response that +is deemed necessary and appropriate to the circumstances. The project team is +obligated to maintain confidentiality with regard to the reporter of an incident. +Further details of specific enforcement policies may be posted separately. + +Project maintainers who do not follow or enforce the Code of Conduct in good +faith may face temporary or permanent repercussions as determined by other +members of the project's leadership. + +## Attribution + +This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4, +available at https://www.contributor-covenant.org/version/1/4/code-of-conduct.html + +[homepage]: https://www.contributor-covenant.org + +For answers to common questions about this code of conduct, see +https://www.contributor-covenant.org/faq diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md new file mode 100644 index 0000000..edc95d0 --- /dev/null +++ b/CONTRIBUTING.md @@ -0,0 +1,33 @@ +# Contributing to gha-aws-oidc-sample + +We're glad you want to make a contribution! + +Fork this repository and send in a pull request when you're finished with your changes. Link any relevant issues in too. + +Take note of the build status of your pull request, only builds that pass will be accepted. Please also keep to our conventions and style so we can keep this repository as clean as possible. + +## License + +By contributing your code, you agree to license your contribution under the terms of the APLv2: [LICENSE](LICENSE) + +All files are released with the Apache 2.0 license. + +If you are adding a new file it should have a header like this: + +``` +/** + * Copyright <> Skyscanner Limited. + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + ``` diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..146e283 --- /dev/null +++ b/LICENSE @@ -0,0 +1,201 @@ + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + +TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + +1. Definitions. + + "License" shall mean the terms and conditions for use, reproduction, + and distribution as defined by Sections 1 through 9 of this document. + + "Licensor" shall mean the copyright owner or entity authorized by + the copyright owner that is granting the License. + + "Legal Entity" shall mean the union of the acting entity and all + other entities that control, are controlled by, or are under common + control with that entity. For the purposes of this definition, + "control" means (i) the power, direct or indirect, to cause the + direction or management of such entity, whether by contract or + otherwise, or (ii) ownership of fifty percent (50%) or more of the + outstanding shares, or (iii) beneficial ownership of such entity. + + "You" (or "Your") shall mean an individual or Legal Entity + exercising permissions granted by this License. + + "Source" form shall mean the preferred form for making modifications, + including but not limited to software source code, documentation + source, and configuration files. + + "Object" form shall mean any form resulting from mechanical + transformation or translation of a Source form, including but + not limited to compiled object code, generated documentation, + and conversions to other media types. + + "Work" shall mean the work of authorship, whether in Source or + Object form, made available under the License, as indicated by a + copyright notice that is included in or attached to the work + (an example is provided in the Appendix below). + + "Derivative Works" shall mean any work, whether in Source or Object + form, that is based on (or derived from) the Work and for which the + editorial revisions, annotations, elaborations, or other modifications + represent, as a whole, an original work of authorship. For the purposes + of this License, Derivative Works shall not include works that remain + separable from, or merely link (or bind by name) to the interfaces of, + the Work and Derivative Works thereof. + + "Contribution" shall mean any work of authorship, including + the original version of the Work and any modifications or additions + to that Work or Derivative Works thereof, that is intentionally + submitted to Licensor for inclusion in the Work by the copyright owner + or by an individual or Legal Entity authorized to submit on behalf of + the copyright owner. For the purposes of this definition, "submitted" + means any form of electronic, verbal, or written communication sent + to the Licensor or its representatives, including but not limited to + communication on electronic mailing lists, source code control systems, + and issue tracking systems that are managed by, or on behalf of, the + Licensor for the purpose of discussing and improving the Work, but + excluding communication that is conspicuously marked or otherwise + designated in writing by the copyright owner as "Not a Contribution." + + "Contributor" shall mean Licensor and any individual or Legal Entity + on behalf of whom a Contribution has been received by Licensor and + subsequently incorporated within the Work. + +2. Grant of Copyright License. Subject to the terms and conditions of + this License, each Contributor hereby grants to You a perpetual, + worldwide, non-exclusive, no-charge, royalty-free, irrevocable + copyright license to reproduce, prepare Derivative Works of, + publicly display, publicly perform, sublicense, and distribute the + Work and such Derivative Works in Source or Object form. + +3. Grant of Patent License. Subject to the terms and conditions of + this License, each Contributor hereby grants to You a perpetual, + worldwide, non-exclusive, no-charge, royalty-free, irrevocable + (except as stated in this section) patent license to make, have made, + use, offer to sell, sell, import, and otherwise transfer the Work, + where such license applies only to those patent claims licensable + by such Contributor that are necessarily infringed by their + Contribution(s) alone or by combination of their Contribution(s) + with the Work to which such Contribution(s) was submitted. If You + institute patent litigation against any entity (including a + cross-claim or counterclaim in a lawsuit) alleging that the Work + or a Contribution incorporated within the Work constitutes direct + or contributory patent infringement, then any patent licenses + granted to You under this License for that Work shall terminate + as of the date such litigation is filed. + +4. Redistribution. You may reproduce and distribute copies of the + Work or Derivative Works thereof in any medium, with or without + modifications, and in Source or Object form, provided that You + meet the following conditions: + + (a) You must give any other recipients of the Work or + Derivative Works a copy of this License; and + + (b) You must cause any modified files to carry prominent notices + stating that You changed the files; and + + (c) You must retain, in the Source form of any Derivative Works + that You distribute, all copyright, patent, trademark, and + attribution notices from the Source form of the Work, + excluding those notices that do not pertain to any part of + the Derivative Works; and + + (d) If the Work includes a "NOTICE" text file as part of its + distribution, then any Derivative Works that You distribute must + include a readable copy of the attribution notices contained + within such NOTICE file, excluding those notices that do not + pertain to any part of the Derivative Works, in at least one + of the following places: within a NOTICE text file distributed + as part of the Derivative Works; within the Source form or + documentation, if provided along with the Derivative Works; or, + within a display generated by the Derivative Works, if and + wherever such third-party notices normally appear. The contents + of the NOTICE file are for informational purposes only and + do not modify the License. You may add Your own attribution + notices within Derivative Works that You distribute, alongside + or as an addendum to the NOTICE text from the Work, provided + that such additional attribution notices cannot be construed + as modifying the License. + + You may add Your own copyright statement to Your modifications and + may provide additional or different license terms and conditions + for use, reproduction, or distribution of Your modifications, or + for any such Derivative Works as a whole, provided Your use, + reproduction, and distribution of the Work otherwise complies with + the conditions stated in this License. + +5. Submission of Contributions. Unless You explicitly state otherwise, + any Contribution intentionally submitted for inclusion in the Work + by You to the Licensor shall be under the terms and conditions of + this License, without any additional terms or conditions. + Notwithstanding the above, nothing herein shall supersede or modify + the terms of any separate license agreement you may have executed + with Licensor regarding such Contributions. + +6. Trademarks. This License does not grant permission to use the trade + names, trademarks, service marks, or product names of the Licensor, + except as required for reasonable and customary use in describing the + origin of the Work and reproducing the content of the NOTICE file. + +7. Disclaimer of Warranty. Unless required by applicable law or + agreed to in writing, Licensor provides the Work (and each + Contributor provides its Contributions) on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or + implied, including, without limitation, any warranties or conditions + of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A + PARTICULAR PURPOSE. You are solely responsible for determining the + appropriateness of using or redistributing the Work and assume any + risks associated with Your exercise of permissions under this License. + +8. Limitation of Liability. In no event and under no legal theory, + whether in tort (including negligence), contract, or otherwise, + unless required by applicable law (such as deliberate and grossly + negligent acts) or agreed to in writing, shall any Contributor be + liable to You for damages, including any direct, indirect, special, + incidental, or consequential damages of any character arising as a + result of this License or out of the use or inability to use the + Work (including but not limited to damages for loss of goodwill, + work stoppage, computer failure or malfunction, or any and all + other commercial damages or losses), even if such Contributor + has been advised of the possibility of such damages. + +9. Accepting Warranty or Additional Liability. While redistributing + the Work or Derivative Works thereof, You may choose to offer, + and charge a fee for, acceptance of support, warranty, indemnity, + or other liability obligations and/or rights consistent with this + License. However, in accepting such obligations, You may act only + on Your own behalf and on Your sole responsibility, not on behalf + of any other Contributor, and only if You agree to indemnify, + defend, and hold each Contributor harmless for any liability + incurred by, or claims asserted against, such Contributor by reason + of your accepting any such warranty or additional liability. + +END OF TERMS AND CONDITIONS + +APPENDIX: How to apply the Apache License to your work. + + To apply the Apache License to your work, attach the following + boilerplate notice, with the fields enclosed by brackets "{}" + replaced with your own identifying information. (Don't include + the brackets!) The text should be enclosed in the appropriate + comment syntax for the file format. We also recommend that a + file or class name and description of purpose be included on the + same "printed page" as the copyright notice for easier + identification within third-party archives. + +Copyright {yyyy} {name of copyright owner} + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. diff --git a/README.md b/README.md new file mode 100644 index 0000000..dc1b6d7 --- /dev/null +++ b/README.md @@ -0,0 +1,159 @@ +# gha-aws-oidc-sample +End-to-end demonstration of enforcing per-repo privileges on AWS with GitHub Actions OIDC. + +## Context and problem statement +We'd like to use [GitHub Actions' OIDC IdP](https://docs.github.com/en/enterprise-cloud@latest/actions/deployment/security-hardening-your-deployments/configuring-openid-connect-in-cloud-providers) for directly presenting repository identities to AWS for authentication+authorisation control, hoping we'll be able to mostly get rid of AWS Access Key secrets and IAM Instance Roles across our CI estate. + +Unfortunately, despite AWS' support for OIDC with IAM and GitHub Actions' OIDC IdP, the AWS community has experienced long-standing issues with presenting a repository identity for use during IAM policy evaluation. + +
+Utopia: Directly enforce resource naming in IAM based on OIDC claims + +### Utopia: Directly enforce resource naming in IAM based on OIDC claims + +[![Diagram: Utopia](docs/diagram-utopia.png)](docs/diagram-utopia.pdf) + +> While directly enforcing resource naming in IAM based on OIDC claims would be the best option toward reducing the number of internally-managed components in the security critical path, we’re unable to take this option today due to parallel blockers on GitHub and AWS' issuance and de-marshalling of OIDC JWT tokens (respectively). +> +> +> #### Blockers +> +> * https://github.com/orgs/community/discussions/12031 +> * https://github.com/aws-actions/configure-aws-credentials/issues/419 +> +> (see also, Aidan Steele's 2021 blog post: [AWS IAM OIDC IDPs need more controls](https://awsteele.com/blog/2021/10/12/aws-iam-oidc-idps-need-more-controls.html)) + +
+ + +In this repository, we show off using a Reusable Workflow to provide AWS IAM with repository information through an [inline session policy](https://github.com/aws-actions/configure-aws-credentials#inline-session-policies) while also enforcing use of the Reusable Workflow through a [customised `sub` claim](https://docs.github.com/en/enterprise-cloud@latest/actions/deployment/security-hardening-your-deployments/about-security-hardening-with-openid-connect). + +Hoping for a future where either AWS or GitHub are able to unblock us, we also call out future migration ‘escape path’s against our presented workaround. + + +## Contents +* [cfn.yaml](cfn.yaml): CloudFormation template + * [AWS::IAM::OIDCProvider](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-iam-oidcprovider.html), to configure GitHub Actions' OIDC provider with AWS + * [AWS::S3::Bucket](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-s3-bucket.html), to hold files uploaded by GitHub Actions + * [AWS::IAM::Role](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-iam-role.html), to allow a reusable workflow broad access to the aforementioned S3 bucket + +* [.github/workflows/reusable-s3.yaml](.github/workflows/reusable-s3.yaml): Reusable Workflow + * [aws-actions/configure-aws-credentials](https://github.com/aws-actions/configure-aws-credentials), to establish a session with AWS IAM/STS + * [actions/download-artifact](https://github.com/actions/download-artifact), to retrieve artifacts uploaded by earlier jobs + * [AWS CLI](https://aws.amazon.com/cli/), for uploading artifacts to AWS S3 + +* [.github/workflows/main-s3.yaml](.github/workflows/main-s3.yaml): Unit test workflow + * Demonstrate creating a test file and uploading it to S3, under a bucket prefix determined by the repo name + +## Deploying +1. Create a new GitHub repo + +2. Configure fork / branch protection settings (see also, § [Guarding against malicious forks](README.md#guarding-against-malicious-forks)) + +2. Make a GitHub REST API call to [Set the customization template for an OIDC subject claim for a repository](https://docs.github.com/en/enterprise-cloud@latest/rest/actions/oidc?apiVersion=2022-11-28#set-the-customization-template-for-an-oidc-subject-claim-for-a-repository) + +```bash +curl --request PUT \ + --url https://api.github.com/repos/$GH_ORG/$GH_REPO/actions/oidc/customization/sub \ + --header 'Accept: application/vnd.github+json' \ + --header 'Authorization: Bearer $GH_TOKEN' \ + --data '{"use_default":false,"include_claim_keys":["repo","context","job_workflow_ref"]}' +``` + +3. Deploy [cfn.yaml](cfn.yaml) with AWS CloudFormation + +4. Update environment variables in [.github/workflows/reusable-s3.yaml](.github/workflows/reusable-s3.yaml) (`BUCKET`, `ROLE_TO_ASSUME`, and `REGION`) to match your AWS account using the CloudFormation outputs + +4. Observe GitHub Actions authenticating to AWS with OIDC before uploading a test file + +## Design: Introduce a Reusable Workflow that enforces resource naming +[![Diagram: Reality - Introduce a Reusable Workflow that enforces resource naming](docs/diagram-reality.png)](docs/diagram-reality.pdf) + +While GitHub Actions doesn’t allow generally customising its OIDC claims format, we can require `job_workflow_ref` be included in the `sub` claim and reference this in an AWS IAM policy to restrict access to a Reusable Workflow managed by our infrastructure team. + +This workflow can then use an [inline session policy](https://github.com/aws-actions/configure-aws-credentials#inline-session-policies) (via [aws-actions/configure-aws-credentials#739](https://github.com/aws-actions/configure-aws-credentials/pull/739)) and provide reduced privileges scoped to the repository identity. + + +#### Escape Path 🏃 + +* Assuming GitHub introduce support for custom OIDC claims: + + * we could emit OIDC claims directly from GitHub in AWS' Session Tags format, obviating our need for the Reusable Workflow’s initial highly privileged policy. + +* Assuming AWS introduce support for reading arbitrary OIDC claims: + + * we could create IAM policies that directly provide reduced privileges based on the repository identity, obviating our need for the Reusable Workflow’s initial highly privileged policy. + + +#### Downsides 😥 + + * We place load bearing security responsibilities upon our Reusable Workflow, significantly increasing the risk of a *[confused deputy problem](https://docs.aws.amazon.com/IAM/latest/UserGuide/confused-deputy.html)* through logic or parameter escaping issues + + +#### Upsides 🚀 + + * We can introduce override logic inside the Reusable Workflow for projects that need non-standard AWS resource names + + +## Security Properties +### Reducing Privileges at Runtime + +Since [passing session tags using AssumeRoleWithWebIdentity](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_session-tags.html#id_session-tags_adding-assume-role-idp) requires a proprietary `https://aws.amazon.com/tags` claim [that GHA can't emit as of 2023](https://github.com/orgs/community/discussions/12031), we're unable to immediately rely on session tagging for isolating resources with an IAM role policy. + +Instead, we use the [`github` context](https://docs.github.com/en/enterprise-cloud@latest/actions/learn-github-actions/contexts#github-context) to inject the repository identity into an [inline session policy](https://github.com/aws-actions/configure-aws-credentials#inline-session-policies). + +https://github.com/Skyscanner/gha-aws-oidc-sample/blob/main/.github/workflows/reusable-s3.yaml#L55-L89 + +This happens during a single call to [AssumeRoleWithWebIdentity](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithWebIdentity.html), so we don't expect e.g., early crashes in our Reusable Workflow to be useful for privilege escalation. + +We also use the `RoleSessionName` parameter ([on AssumeRoleWithWebIdentity](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithWebIdentity.html)) to ensure the repository identity is recorded in CloudTrail. + +### Requiring use of our Reusable Workflow +> [!NOTE] +> As of 2023, this requires a per-repo GitHub REST API call to [Set the customization template for an OIDC subject claim for a repository](https://docs.github.com/en/enterprise-cloud@latest/rest/actions/oidc?apiVersion=2022-11-28#set-the-customization-template-for-an-oidc-subject-claim-for-a-repository). +> +> We've observed just calling [Set the customization template for an OIDC subject claim for an organization](https://docs.github.com/en/enterprise-cloud@latest/rest/actions/oidc?apiVersion=2022-11-28#set-the-customization-template-for-an-oidc-subject-claim-for-an-organization) isn't enough to include `job_workflow_ref` in the `sub` claim. +> +> Trying to access AWS from a repository with an uncustomised OIDC subject claim template (or trying to assume the IAM role without using the Reusable Workflow) will cause AWS to return `Error: Not authorized to perform sts:AssumeRoleWithWebIdentity`. +> +> --- +> **GitHub Docs** [Example: Requiring a reusable workflow](https://docs.github.com/en/enterprise-cloud@latest/actions/deployment/security-hardening-your-deployments/about-security-hardening-with-openid-connect) + +In an effort to reduce the attack surface for our (initially) widely privileged IAM role, we make use of GitHub Actions OIDC IdP's [subject claim customisation](https://docs.github.com/en/enterprise-cloud@latest/actions/deployment/security-hardening-your-deployments/about-security-hardening-with-openid-connect#customizing-the-subject-claims-for-an-organization-or-repository) to indicate our Reusable Workflow's identity. This `job_workflow_ref` claim is then declared as a condition to our `AssumeRolePolicyDocument`. + +https://github.com/Skyscanner/gha-aws-oidc-sample/blob/main/cfn.yaml#L55-L66 + + +### Guarding against malicious forks +We leverage "[Approving workflow runs from private forks](https://docs.github.com/en/enterprise-cloud@latest/actions/managing-workflow-runs/approving-workflow-runs-from-private-forks)" to ensure the `sub` claim for `job_workflow_ref` can't be confused through unexpected PRs against our Reusable Workflow. + +Additionally, we use [branch protection rules](https://docs.github.com/en/enterprise-cloud@latest/repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/managing-a-branch-protection-rule#creating-a-branch-protection-rule) to ensure only our infrastructure team is able to create new branches that are accepted by our IAM role's `job_workflow_ref` condition. + + +### Separating execution environments +> [!WARNING] +> If your reusable workflow provides a customer execution environment (e.g., for Docker image +> building), you **must** ensure the `ACTIONS_RUNTIME_TOKEN` and `ACTIONS_ID_TOKEN_REQUEST_URL` +> environment variables are not accessible. +> +> --- +> **GitHub Docs** Configuring OpenID Connect in cloud providers § [Using custom actions](https://docs.github.com/en/enterprise-cloud@latest/actions/deployment/security-hardening-your-deployments/configuring-openid-connect-in-cloud-providers#using-custom-actions) + +GitHub Actions allows jobs to request an OIDC token by making a request to `ACTIONS_ID_TOKEN_REQUEST_URL` using `ACTIONS_RUNTIME_TOKEN`. + +If these environment variables are accesible by a customer execution environment hosted by your reusable workflow, an attacker could achieve privilege escalation by asking GitHub Actions for a fresh OIDC token and skipping the `inline-session-policy`. + +## Further Reading + + * Aidan Steele's 2021 blog post: [AWS IAM OIDC IDPs need more controls](https://awsteele.com/blog/2021/10/12/aws-iam-oidc-idps-need-more-controls.html) + * https://github.com/orgs/community/discussions/12031 + * https://github.com/aws-actions/configure-aws-credentials/issues/419 + * **AWS Docs** [Available keys for AWS web identity federation](https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_iam-condition-keys.html#condition-keys-wif) + * **AWS Docs** [Passing session tags using AssumeRoleWithWebIdentity](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_session-tags.html#id_session-tags_adding-assume-role-idp) (not available with GHA as of 2023) + * **AWS Docs** [The confused deputy problem](https://docs.aws.amazon.com/IAM/latest/UserGuide/confused-deputy.html) + * **GitHub Docs** [Configuring OpenID Connect in Amazon Web Services](https://docs.github.com/en/enterprise-cloud@latest/actions/deployment/security-hardening-your-deployments/configuring-openid-connect-in-amazon-web-services) + * **GitHub Docs** Configuring OpenID Connect in cloud providers § [Using custom actions](https://docs.github.com/en/enterprise-cloud@latest/actions/deployment/security-hardening-your-deployments/configuring-openid-connect-in-cloud-providers#using-custom-actions) + * **GitHub Docs** [Example: Requiring a reusable workflow](https://docs.github.com/en/enterprise-cloud@latest/actions/deployment/security-hardening-your-deployments/about-security-hardening-with-openid-connect#example-requiring-a-reusable-workflow) + * **GitHub Docs** [`github` context](https://docs.github.com/en/enterprise-cloud@latest/actions/learn-github-actions/contexts#github-context) + * **configure-aws-credentials Docs** [Inline session policies](https://github.com/aws-actions/configure-aws-credentials#inline-session-policies) + * **configure-aws-credentials Docs** [Session tagging](https://github.com/aws-actions/configure-aws-credentials#session-tagging) diff --git a/SECURITY.md b/SECURITY.md new file mode 100644 index 0000000..e52224d --- /dev/null +++ b/SECURITY.md @@ -0,0 +1,4 @@ +# Vulnerability Disclosure Policy +Keeping traveller’s information safe and secure is a top priority and a core company value for us at Skyscanner. We highly appreciate the efforts of external security researchers who contribute to the safety of Skyscanner's users. + +To submit a vulnerability you’ve found, you will first need to [sign up for free as a Bugcrowd researcher](https://bugcrowd.com/user/sign_up) and then submit your findings directly to our [programme](https://bugcrowd.com/skyscanner). We won’t consider any vulnerabilities submitted outside of Bugcrowd. diff --git a/cfn.yaml b/cfn.yaml new file mode 100644 index 0000000..4208575 --- /dev/null +++ b/cfn.yaml @@ -0,0 +1,94 @@ +--- +# Copyright 2023 Skyscanner Limited. + +# Licensed under the Apache License, Version 2.0 (the "License"); +# you may not use this file except in compliance with the License. +# You may obtain a copy of the License at + +# http://www.apache.org/licenses/LICENSE-2.0 + +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, +# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +# See the License for the specific language governing permissions and +# limitations under the License. + +AWSTemplateFormatVersion: 2010-09-09 +Description: Sample IAM roles for Github Actions + +Parameters: + GitHubOrg: + Type: String + Description: "Username for your GitHub.com organisation or personal account (example: `Skyscanner`)" + GitHubReusableWorkflow: + Type: String + Description: "Constraint for job_workflow_ref, should point to your Reusable Workflow (example: `Skyscanner/gha-aws-oidc-sample/.github/workflows/reusable-s3.yaml@*`)" + +Outputs: + StaticContentBucketName: + Description: Name of the created S3 bucket. + Value: !Ref StaticContentBucket + StaticContentRoleArn: + Description: ARN for the created IAM role. + Value: !GetAtt StaticContentRole.Arn + +Resources: + GithubOidc: + Type: AWS::IAM::OIDCProvider + Properties: + Url: https://token.actions.githubusercontent.com + ClientIdList: + - sts.amazonaws.com + ThumbprintList: + # not used for `token.actions.githubusercontent.com` + # see also: https://github.com/aws-actions/configure-aws-credentials#sample-iam-oidc-cloudformation-template + - ffffffffffffffffffffffffffffffffffffffff + + StaticContentBucket: + Type: AWS::S3::Bucket + + StaticContentRole: + Type: AWS::IAM::Role + Properties: + AssumeRolePolicyDocument: + Version: "2012-10-17" + Statement: + - Effect: Allow + Action: sts:AssumeRoleWithWebIdentity + Principal: + Federated: !Ref GithubOidc + Condition: + StringEquals: + token.actions.githubusercontent.com:aud: "sts.amazonaws.com" + StringLike: + token.actions.githubusercontent.com:sub: !Sub "repo:${GitHubOrg}/*:job_workflow_ref:${GitHubReusableWorkflow}" + Policies: + - PolicyName: ListStaticContent + PolicyDocument: + Version: "2012-10-17" + Statement: + - Effect: Allow + Action: + - s3:ListBucket + Resource: !GetAtt StaticContentBucket.Arn + - Effect: Allow + Action: + - "ecr:GetAuthorizationToken" + Resource: + - "*" + - PolicyName: PushStaticContent + PolicyDocument: + Version: "2012-10-17" + Statement: + - Action: + - s3:GetObject + - s3:GetObjectAcl + - s3:GetObjectVersion + - s3:PutObject + - s3:PutObjectAcl + - s3:DeleteObject + - s3:DeleteObjectVersion + Effect: Allow + Resource: + - !GetAtt StaticContentBucket.Arn + - !Sub "${StaticContentBucket.Arn}/*" diff --git a/docs/diagram-reality.pdf b/docs/diagram-reality.pdf new file mode 100644 index 0000000..1cb8514 Binary files /dev/null and b/docs/diagram-reality.pdf differ diff --git a/docs/diagram-reality.png b/docs/diagram-reality.png new file mode 100644 index 0000000..9c99668 Binary files /dev/null and b/docs/diagram-reality.png differ diff --git a/docs/diagram-utopia.pdf b/docs/diagram-utopia.pdf new file mode 100644 index 0000000..b320667 Binary files /dev/null and b/docs/diagram-utopia.pdf differ diff --git a/docs/diagram-utopia.png b/docs/diagram-utopia.png new file mode 100644 index 0000000..44d8ac2 Binary files /dev/null and b/docs/diagram-utopia.png differ