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fkie_cve-2026-111061

2026-10-26T12:41:14.717279+00:00

russh is a Rust SSH client and server library that includes an SSH agent protocol implementation. Prior to 0.64.1, the agent server spawns a separate long-lived task for every SSH_AGENT_CONSTRAIN_LIFETIME record in a constrained add-key request. The loop accepts repeated lifetime records, clones the key blob into each task, and does not roll back tasks when later constraint parsing fails. An attacker that can speak the agent protocol locally or through agent forwarding can exhaust memory and tasks until the agent process is starved or terminated, denying SSH agent service. This issue is fixed in version 0.64.1.

GHSA-4wc5-f2rc-q74m — russh: Unbounded memory allocation in agent protocol server via crafted constraint records

2026-10-26T12:41:14.717356+00:00

Affected: crates.io: russh

### Summary

`russh_keys::agent::server::add_key` (`russh/src/keys/agent/server.rs:271-319`) spawns a dedicated tokio task for every 5-byte `SSH_AGENT_CONSTRAIN_LIFETIME` record attached to an added key, each cloning the key blob and sleeping for the declared lifetime (up to ~136 years). The loop has no per-request task budget, and spawned tasks are not rolled back when the overall request fails. Repeating one constrained add-key message over an agent connection converts wire bytes into resident tasks and heap at roughly 141x amplification: in our measurement 10.2 MiB of protocol traffic produced ~2,096,120 live tasks and +1,447,856 KiB RSS, while the same traffic sent as unconstrained add-key requests cost +268 KiB. An attacker reaching the agent socket (a local process, or a remote SSH server the user connects to with agent forwarding, since russh clients accept the `auth-agent@openssh.com` channel by default at `russh/src/client/mod.rs:2686`) can exhaust the agent process's memory and task capacity with a renewable, cheap request stream. Verified on russh HEAD efa9a03 (v0.63.3-10, 2026-10-01).

### Details

```rust // russh/src/keys/agent/server.rs:271-319 (add_key, constraint loop) while let Ok(t) = u8::decode(r) { match t { SSH_AGENT_CONSTRAIN_LIFETIME => { let lifetime = u32::decode(r)?; ... tokio::spawn({ let key = key.clone; async move { tokio::time::sleep(...lifetime...).await; /* remove key */ } }); } ... ```

Each lifetime record clones the key blob int…

UBUNTU-CVE-2026-111061

2026-10-26T12:41:14.717433+00:00

Affected: Ubuntu:26.10: rust-russh

(russh is a Rust SSH client and server library that includes an SSH age ...)