russh: Agent server never calls `Agent::confirm`, so keys added with the confirm constraint (`ssh-add -c`) sign without confirmation

Summary

russh is a Rust SSH client and server library that includes an SSH agent protocol implementation. From 0.50.0-beta.12 until 0.65.0, the agent server's Connection::try_sign path in russh/src/keys/agent/server.rs recognizes SSH_AGENT_CONSTRAIN_CONFIRM but returns a hard-coded successful result instead of calling Agent::confirm. In applications that override Agent::confirm to require user approval or another policy check, a process that can reach the agent socket, including the remote side of a forwarded agent, can use a key added through ssh-add -c without that check and can authenticate or sign data as the user while the key remains loaded. The separate Agent::confirm_request hook still runs for every signing request, so checks implemented there remain effective, and implementations that retain the default always-successful Agent::confirm do not lose an approval check through this regression. This issue is fixed in version 0.65.0.

Remediation

1. Inventory every russh deployment, including staging.
2. Upgrade russh to 0.65.
3. Confirm the running version after the upgrade.

References

• Advisoryhttps://github.com/advisories/GHSA-vp5q-ff62-jwqv
• Referencehttps://github.com/Eugeny/russh/commit/3e04597dc54e36bfc85c21996f7d8d9d224e9826
• Referencehttps://github.com/Eugeny/russh/commit/62db6e7defd6d244159da962ccccb029e785ce0f
• Referencehttps://github.com/Eugeny/russh/releases/tag/v0.65.0
• Referencehttps://github.com/Eugeny/russh/security/advisories/GHSA-vp5q-ff62-jwqv
• Referencehttps://nvd.nist.gov/vuln/detail/CVE-2026-116794