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

Vulnerability summary

CVE-2026-116774 is a medium (CVSS 4.3) Uncontrolled Resource Consumption vulnerability in eugeny russh. EPSS estimates a 0.26% chance of exploitation in the next 30 days, higher than 17.7% of scored vulnerabilities.

Timeline

1. 27-10-2026
   PublishedVulnerability first disclosed.
2. 28-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.
• CWE-835Loop with Unreachable Exit ConditionThe product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.