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Any signed GitHub commit can be copied, without the author's secret key, creating a distinct commit with an identical tree, metadata, a valid signature, and a "Verified" badge (www.internationalcyberdigest.com)
submitted 4 months ago by to c/security@lemmy.ml
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PoC: https://github.com/JakeGinesin/git-chain-malleator

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[–] 3 points 4 months ago* (5 children)

I don't understand. Why does having two commit IDs with the exact same code cause problems.

A green “Verified” badge on GitHub is supposed to mean that a trusted author signed it

The author did sign it. It is the exact same code.

An attacker can reissue the same signed code under a fresh ID that’s still verified to slip past.

To split past what? At best it seems that they would be able to have a different ID for the exact same code, which seems harmless? Slightly confusing at worst.

Nix also doesn't use PGP signatures, it requires a separate hash of the resulting commit (the files with the .git directory stripped by default).

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  • [–] [S] 1 point 4 months ago (4 children)

    Right, it's not a serious exploit which would allow changing code, but it does allow compromising integrity because changing the id mutates history.

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  • [–] 1 point 4 months ago (3 children)

    It doesn't mutate history. It just creates a new branch of history in their own fork. Just like any new commit would do.

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  • [–] [S] 0 points 4 months ago (2 children)

    but looking back you have no way to tell which branch is the real one

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  • [–] 1 point 4 months ago (1 child)

    Please explain what you mean and how this could be abused. What does "real" mean in this context? They both have the same code. It would probably help if you can provide a specific attack that could actually cause harm rather than just stating facts that have unclear risk.

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  • [–] [S] 0 points 4 months ago

    My understanding is that you'd end up with two divergent histories and you can't tell which one is the original. I don't know how it could be abused off top of my head, but generally speaking people tend to find ways to abuse these kinds of things.

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