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

russh · Missing authorization · CWE-862

Affectedrussh

FixNo fix listed yet.

PublishedOct 28, 17:06 · GitHub_M

ScoredOct 28 · 8.3 · GitHub_M

Exploit code publicNone known · checked 21:18 UTC

ExploitedNone known · CISA KEV checked 22:09 UTC

What we know

No known exploitation. CISA KEV, checked 22:09 UTC.

No public exploit code known. Exploit-DB, Metasploit, Nuclei, checked 21:18 UTC.

An attacker needs local access to the machine. CVSS: local.

A successful attack can change data. CVSS impact.

Description

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.

From GitHub_M

Affected and fixed versions

ProductAffectedFixed inrussh< 0.65–

Exploit code

Exploit-DBnone knownMetasploitnone knownNucleinone known

References

github.com/Eugeny/russh/security/advisories/GHSA-vp5q-ff62-jwqv · github.comrefsource_CONFIRM github.com/Eugeny/russh/commit/3e04597dc54e36bfc85c21996f7d8d9d224e9826 · github.comrefsource_MISC github.com/Eugeny/russh/commit/62db6e7defd6d244159da962ccccb029e785ce0f · github.comrefsource_MISC github.com/Eugeny/russh/releases/tag/v0.65.0 · github.comrefsource_MISC

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