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reject nul bytes in ssh certificate key ids and principals - #15970
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alex
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Nov 7, 2026
| # OpenSSH reads the key ID and principals as C strings: it drops a | ||
| # trailing NUL and rejects the certificate for any other NUL. | ||
| key_id, rest = _get_sshstr(rest) | ||
| if b"\x00" in bytes(key_id): |
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why are we converting key_id to bytes? 0 in key_id works fine
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SSHCertificateBuilderandload_ssh_public_identityaccept NUL bytes in a certificate's key ID and principals, but OpenSSH reads both fields as C strings (a trailing NUL is dropped and any other NUL makes the certificate invalid), so a principal ofb"root\x00"is signed and reported as-is here whilessh-keygen -L(OpenSSH 10.5p1) and sshd read it asroot; both now raiseValueError, with regression vectors for the loader.