Bug 2543499 (CVE-2026-102822)

Summary: CVE-2026-102822 russh: russh: Denial of Service via improper MAC negotiation with block ciphers
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in russh. This vulnerability allows a remote attacker to cause a Denial of Service (DoS) by terminating active connection tasks. When a connection is configured to permit sessions without a Message Authentication Code (MAC), improper algorithm negotiation allows pairing with block ciphers that require authentication. A remote peer can then send a specially crafted packet that triggers an out-of-bounds indexing error, causing the connection process to crash.
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Description OSIDB Bzimport 2026-09-29 18:40:30 UTC 
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.