Verify backup signature on self-update --rollback#12918
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self-update --rollback restored the newest *-old.phar backup from data-dir without verifying its signature. On systems where data-dir/COMPOSER_HOME is writable by other users, someone could plant a malicious backup that a privileged --rollback would then install over composer.phar. Rollback now downloads the published signature for the backed-up version and verifies the backup against it (reusing the existing self-update verification logic, extracted into verifyPhar()), aborting on a mismatch or an unfetchable signature. Snapshot/dev backups have no published signature, so verification is skipped with a warning and an interactive confirmation prompt. Rollback also warns (and prompts when interactive) if data-dir or the backup file is owned by another user or writable by others, and the docs now note that data-dir and COMPOSER_HOME must be treated as trusted, only-owner-writable locations.
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PrinsFrank
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Jun 3, 2026
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Nice! I like the very thorough fix!
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composer self-update --rollbackrestored the newest*-old.pharbackup fromdata-dirand installed it overcomposer.pharwithout verifying its signature —rollback()only ranvalidatePhar()(a structural Phar parse), unlike the normal update path which verifies against the published signature.On a system where
data-dir/COMPOSER_HOMEis writable by other (less-privileged) users, someone could plant a malicious*-old.phar; a privileged user runningself-update --rollbackwould then install it over the composer binary, leading to code execution as that user. The preconditions make this low severity, but it's cheap to close.