russh server userauth state is not reset when authentication principal changes

published 2026-05-29 5 mo ago modified 2026-09-10 1 mo ago also GHSA-hpv4-5h6f-wqr3 , EUVD-2026-36126

cvss: 5.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits: 0; none known

Russh is a Rust SSH client & server library. From version 0.34.0-beta.1 to before version 0.61.0, the russh server authentication path keeps internal userauth state across SSH_MSG_USERAUTH_REQUEST messages without separating that state when the request principal changes. RFC 4252 allows the user name and service name fields to change between authentication requests. The issue is not that such changes are invalid. The issue is that russh-owned authentication state, such as remaining methods, partial-success state, and in-progress method state, can remain associated with the connection and then influence a later request for a different (user, service). This is an internal library state mismatch. This issue has been patched in version 0.61.0.

Patch / fix

fixed in 1 distros 1

crates.io russh 0.61.0

rust-russh Debian 14 0.64.1-1

debian advisories DEBIAN-CVE-2026-46705

CISA SSVC

Exploitation: Proof of concept is public
Automatable: yes
Technical impact: partial
Assessed: 4 mo ago (2026-06-11)

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/Eugeny/russh/security/advisories/GHSA-hpv4-5h6f-wqr3 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
GitHub	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
crates.io	russh	>=0.34.0-beta.1, <0.61.0	0.61.0

Affected products

Eugeny russh

Classification

Weakness

CWE-287 Improper Authentication

References

github.com /Eugeny/russh/security/advisories/GHSA-hpv4-5h6f-wqr3
exploit, web
nvd.nist.gov /vuln/detail/CVE-2026-46705
advisory
github.com /Eugeny/russh
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary