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[Bug 3675] CASignatureAlgorithms should be verified before verifying signatures
https://bugzilla.mindrot.org/show_bug.cgi?id=3675

Sam James <sam@gentoo.org> changed:

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[Bug 3675] CASignatureAlgorithms should be verified before verifying signatures [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=3675

Luke Simmons <luke5083@live.com> changed:

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[Bug 3675] CASignatureAlgorithms should be verified before verifying signatures [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=3675

Bertrand Jacquin <bertrand@jacquin.bzh> changed:

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[Bug 3675] CASignatureAlgorithms should be verified before verifying signatures [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=3675

Ismail Donmez <ismail@i10z.com> changed:

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[Bug 3675] CASignatureAlgorithms should be verified before verifying signatures [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=3675

felix@eckhofer.com <felix@eckhofer.com> changed:

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[Bug 3675] CASignatureAlgorithms should be verified before verifying signatures [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=3675

Benjamin Gilbert <bgilbert@backtick.net> changed:

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[Bug 3675] CASignatureAlgorithms should be verified before verifying signatures [ In reply to ]
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github@kalvdans.no-ip.org changed:

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[Bug 3675] CASignatureAlgorithms should be verified before verifying signatures [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=3675

--- Comment #4 from Andres Freund <andres@anarazel.de> ---
> On the one hand it feels a bit like trying to fight the last battle, but on the other it is a meaningful attack surface reduction.

Agreed on both points.

Thanks for the quick writing of the patch!


I don't know the openssh codebase well, so my ability to provide review
is limited.

I think there might still be one path "unprotected" after this.
userauth_hostbased() uses sshkey_from_blob() and
a) checks options.hostbased_accepted_algos afterwards
b) uses sshkey_from_blob(), not sshkey_from_blob_expect_type(), with a
subsequent check of the certificate type


Another thing I noticed is that it might end up being a bit harder to
debug some of the error paths after the change, due to going from
specific error messages to more generic error codes. OTOH, it seems
unlikely that these paths are encountered outside of attacks.

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