A russh SSH server accepts a publickey authentication whose signature uses a different algorithm than the one named in the request

russh is a Rust SSH client and server library. From version 0.34.0-beta.1 until version 0.64.0, its SSH server does not require the signature algorithm in a public-key authentication signature to match the algorithm named in the authentication request. A client possessing an authorized RSA private key can announce  rsa-sha2-512  while supplying a valid  ssh-rsa  SHA-1 signature, bypassing restrictions or producing misleading audit records when applications rely on the requested algorithm. A valid private-key signature remains required, and russh clients are not affected. This issue is fixed in version 0.64.0.

Source published

5 Nov 2026 20:47:35 UTC

Source modified

5 Nov 2026 20:47:35 UTC

Observed here

5 Nov 2026 21:36:21 UTC

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CVSS 4.0 · 2.3 CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N