Bug 2573415 (CVE-2026-128087)

Summary: CVE-2026-128087 russh: russh: Information disclosure via premature callback execution prior to host verification
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in russh. During the initial key exchange, the library invokes client completion callbacks before verifying the server's host key or certificate. A malicious SSH server can exploit this issue to trigger early data processing or secondary-channel communication before establishing trust, potentially leading to unauthorized information disclosure.
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Description OSIDB Bzimport 2026-11-13 19:11:20 UTC 
russh is a Rust SSH client and server library that includes an SSH agent protocol implementation. From version 0.55.0 until version 0.65.1, the initial key exchange invokes client::Handler::kex_done() with the raw shared secret before check_server_key() accepts the server host key or certificate. A malicious SSH server can therefore trigger application-defined secondary-channel initialization or early data handling even when the server identity is subsequently rejected. Ordinary clients that keep the callback's no-op default or independently defer callback-derived actions until trust is confirmed are not affected. This issue is fixed in version 0.65.1.