russh: negotiating a MAC-requiring block cipher (CTR/CBC) with mac=none causes a slice-index-out-of-range panic

[ Why it matters ]Priority signals

• Public proof-of-concept exploit exists (CISA SSVC)

[ Description ]Official description

Russh is a Rust SSH client and server library. Prior to 0.63.1, a connection configured to permit mac=none can negotiate it with a MAC-requiring CTR or CBC block cipher because the selection logic validates needs_mac() only when MAC selection fails. A remote peer can then send a packet with a decrypted length of zero, causing russh/src/cipher/mod.rs to shrink the previously read block before indexing buffer.buffer[16..], which panics and terminates the connection task. This issue is fixed in version 0.63.1.

[ Fixes ]Fixes and patches

• russh 0.63.1Fixed version · GitHub Advisories · rust package russh: upgrade to 0.63.1 or later (affected <= 0.63.0)

[ Packages ]Affected open-source packages

• russh rustAffected <= 0.63.0 · fixed in 0.63.1 · GHSA-p8qx-h547-fjw9

[ References ]References

• github.com/Eugeny/russh/commit/2885385abfee279092a41d80c6cb6ac367353159
• github.com/Eugeny/russh/releases/tag/v0.63.1
• github.com/Eugeny/russh/security/advisories/GHSA-p8qx-h547-fjw9