Add compile-time validation for dangerous property names in expressions#14829
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Add compile-time validation for dangerous property names in expressions#14829
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Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
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[WIP] Add compiler validation for forbidden field names in expressions
Add compile-time validation for dangerous property names in expressions
Feb 10, 2026
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Pull request overview
Adds compile-time validation to block dangerous JavaScript property names in GitHub Actions expressions (e.g., constructor, __proto__) to prevent prototype-pollution style access patterns, aligning compile-time checks with existing runtime protections.
Changes:
- Introduces a
DangerousPropertyNamesblocklist constant. - Adds
validateExpressionForDangerousProps()and runs it early during single-expression validation. - Expands expression safety tests to cover blocked properties and end-to-end markdown validation.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| pkg/workflow/expression_validation.go | Adds dangerous-property detection and integrates it into expression validation flow. |
| pkg/constants/constants.go | Defines the dangerous property name blocklist used by the validator. |
| pkg/workflow/expression_safety_test.go | Adds unit + integration-style tests for dangerous property validation. |
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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
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This reverts commit c10cefe. The commit introduced undefined regex variables (dangerousPropSplitRe, numericIndexRe) that were never added to the var block, breaking compilation. Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
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Add compile-time validation for dangerous property names in expressions
Extends the runtime protection from #14826 by blocking dangerous JavaScript property names at compile time. Prevents prototype pollution attacks via expressions like
${{ github.constructor }}or${{ inputs.__proto__ }}.Changes
DangerousPropertyNamesinpkg/constants/constants.golists 13 blocked property names (constructor, proto, prototype, toString, valueOf, etc.)validateExpressionForDangerousProps()inpkg/workflow/expression_validation.goparses dot/bracket notation and checks property names against the blocklistvalidateSingleExpression()before other checksExample
Compilation now fails with a clear error:
Safe expressions continue to work:
${{ github.actor }} ✓ ${{ github.event.issue.number }} ✓ ${{ needs.job.outputs.result }} ✓💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.