fix: derive roll write target from trusted state, not untrusted PRs#198
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dsanders11 merged 2 commits intoJun 25, 2026
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During a roll, the bot listed all open PRs whose base is the branch being rolled and whose title starts with "chore: bump node"/"chore: bump chromium", then called updateDepsFile with branch = pr.head.ref. Any GitHub user can open such a PR from a fork, where head.ref is just the fork's branch name. By naming a fork branch after one of the bot's own roll branches (e.g. roller/chromium/35-x-y), an attacker could steer the privileged GitHub App into reading from and committing a DEPS change onto that branch, and have their PR's title/body/labels rewritten by the bot. The branch the bot reads from and commits to is now derived solely from trusted state it created itself (roller/<target>/<electron branch>). Each candidate PR must originate from a branch in the electron/electron repo (not a fork) and be named exactly as the bot names its roll branches before any privileged write, pulls.update, or updateLabels call runs. Attacker-controlled fields (head ref, title, body) can no longer select the write target or receive bot mutations. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01QLpSSfaSgt232HGpNNQ6iZ
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Should we also check the author of the PR is electron-roller[bot]?
Addresses review feedback: in addition to verifying that the PR head lives in the electron/electron repo and is named exactly as the bot names its roll branches, require the PR author to be the roller bot itself before performing any privileged DEPS write or applying title/label updates. This subsumes the previous trop-login prefix check and adds defense in depth so that none of a PR's attacker-controllable fields (author, head ref, title, body) can select the target of a privileged commit. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01QLpSSfaSgt232HGpNNQ6iZ
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During a roll, the bot listed all open PRs whose base is the branch being rolled and whose title starts with "chore: bump node"/"chore: bump chromium", then called updateDepsFile with branch = pr.head.ref. Any GitHub user can open such a PR from a fork, where head.ref is just the fork's branch name. By naming a fork branch after one of the bot's own roll branches (e.g. roller/chromium/35-x-y), an attacker could steer the privileged GitHub App into reading from and committing a DEPS change onto that branch, and have their PR's title/body/labels rewritten by the bot.
The branch the bot reads from and commits to is now derived solely from trusted state it created itself (roller//). Each candidate PR must originate from a branch in the electron/electron repo (not a fork) and be named exactly as the bot names its roll branches before any privileged write, pulls.update, or updateLabels call runs. Attacker-controlled fields (head ref, title, body) can no longer select the write target or receive bot mutations.