CVE-2026-116696: russh's SSH agent server is susceptible to unbound allocations via repeated SSH_AGENT_CONSTRAIN_CONFIRM messages
russh is a Rust SSH client and server library that includes an SSH agent protocol implementation. Prior to 0.65.0, russh::keys::agent::server::serve in russh/src/keys/agent/server.rs accepts repeated SSHAGENTCONSTRAINCONFIRM records while adding a key and appends every Constraint::Confirm record to the key's retained constraint vector without a count or memory limit. A process that can connect to the agent socket, including the remote side of a forwarded agent session, can repeatedly add constrained keys and cause renewable memory growth that persists for the process lifetime because keys without a lifetime constraint do not expire. This issue is fixed in version 0.65.0.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
russhto a version that resolves this vulnerability.Fixed in 0.65.0
Event History
Frequently Asked Questions
Who can trigger the memory growth?
Any process able to connect to the SSH agent socket can do so. This includes the remote side of a forwarded agent session.
What does an attacker need to do to exploit this?
The attacker must repeatedly add keys containing SSH_AGENT_CONSTRAIN_CONFIRM records. Each record is retained without a count or memory limit, causing memory use to grow.
Does the memory use go away automatically?
Not for keys without a lifetime constraint. Their accumulated confirm constraints persist for the lifetime of the process.
Which versions are affected and what fixes the issue?
Versions prior to 0.65.0 are affected. Upgrading russh to version 0.65.0 fixes the issue.