Bug 2563035 (CVE-2026-116794)

Summary: CVE-2026-116794 russh: russh: Unauthorized key signing via SSH agent confirmation bypass
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in russh. When processing signing requests for SSH keys configured to require explicit confirmation, the SSH agent server component fails to invoke the confirmation check and automatically returns success. A local process or remote user with access to the forwarded SSH agent socket can exploit this vulnerability to sign data or authenticate as the key holder without the required user approval.
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Description OSIDB Bzimport 2026-10-28 17:33:38 UTC 
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.