What’s Vulnerable › Vulnerabilities

CVE-2026-116774: russh: peer-declared zero maximum packet size permanently stalls channel writes (silent AsyncWrite hang)

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-27 · updated 2026-10-28
• Weakness: CWE-400

Description

russh is a Rust SSH client and server library that includes an SSH agent protocol implementation. From 0.60.0 until 0.65.0, channel-open parsing accepts a peer-declared maximum_packet_size of zero and passes it into ChannelTx::poll_writable in russh/src/channels/io/tx.rs. The Channel::data, Channel::make_writer, and Channel::into_stream asynchronous write paths then calculate a writable size of zero and remain pending forever because window adjustments cannot satisfy a static zero packet maximum. An authenticated client can strand server writes, and a malicious server can strand client writes, allowing affected tasks, channels, and connections to accumulate without surfacing an error. This issue is fixed in version 0.65.0.

Affected products

• Eugeny russh: from 0.60.0, < 0.65.0

References

• https://github.com/Eugeny/russh/commit/39cb9dbaa37caf555d34c6c22efa3bbbff9e186c
• https://github.com/Eugeny/russh/releases/tag/v0.65.0
• https://github.com/Eugeny/russh/security/advisories/GHSA-fw5c-8223-6h42

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