EUVD-2026-36130
GHSA-76r6-x97p-67vr
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Network-reachable pre-auth SSH phase requires no credentials (PR:N) and no user interaction; impact is limited to partial availability with no confidentiality or integrity exposure.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Lifecycle Timeline
2DescriptionCVE.org
Russh is a Rust SSH client & server library. From version 0.34.0-beta.1 to before version 0.61.0, russh did not enforce the SSH identification-string rules as deliberately as OpenSSH. In particular, the server-side identification reader used the same permissive path as the client, allowing pre-banner lines from clients, and the reader did not enforce a bounded number of pre-banner lines. For a library server built on russh, this could allow a remote peer to hold connection setup resources in the cleartext pre-authentication phase with malformed identification input that should have been rejected early. This issue has been patched in version 0.61.0.
AnalysisAI
Resource exhaustion in Russh's SSH server identification-string reader allows unauthenticated remote attackers to hold connection setup resources indefinitely during the cleartext pre-authentication phase. Russh versions 0.34.0-beta.1 through 0.60.x used the same permissive identification reader for both client and server roles, failing to cap the number of pre-banner lines a connecting client could send before the SSH identification string - a constraint OpenSSH enforces strictly per RFC 4253. Any application serving SSH via russh is exposed to this pre-auth resource-holding condition. No public exploit code has been identified at time of analysis, and the vulnerability is not listed in CISA KEV.
Technical ContextAI
The SSH protocol (RFC 4253) defines a strict format for the identification string exchanged at connection setup (e.g., 'SSH-2.0-...'). Servers are permitted to send pre-banner text lines before their identification string; clients are not. Russh (CPE: cpe:2.3:a:eugeny:russh:*:*:*:*:*:*:*:*) incorrectly applied the same permissive reader code path to its server-side identification reader as to the client-side reader. This meant the server accepted pre-banner lines from inbound clients and placed no upper bound on how many such lines could precede the identification string. The root cause is CWE-20 (Improper Input Validation) - specifically, the absence of an input bound check on a streaming network protocol parser during the unauthenticated setup phase. Because this occurs before any cryptographic negotiation, the malformed input triggers resource holding in cleartext with zero authentication overhead for the attacker.
RemediationAI
The vendor-released patch is Russh version 0.61.0, which enforces bounded pre-banner line handling on the server-side identification reader, aligning behavior with OpenSSH and RFC 4253. Upgrade by updating the russh dependency in Cargo.toml to 0.61.0 or later and recompiling. The advisory is at https://github.com/Eugeny/russh/security/advisories/GHSA-76r6-x97p-67vr. For deployments that cannot upgrade immediately, compensating controls include: configuring network-layer connection rate limits per source IP (e.g., via iptables or a load balancer) to reduce the number of concurrent pre-auth resource holders; setting aggressive TCP connection timeouts at the infrastructure level to force-close stalled connections; and restricting SSH listener exposure to known IP ranges where operationally feasible. These controls reduce attack surface but do not eliminate the flaw - patching to 0.61.0 is the definitive fix.
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Same weakness CWE-20 – Improper Input Validation
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External POC / Exploit Code
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