CVE-2026-59851: Libssh: libssh: authentication bypass via missing gssapi principal check

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-21 · updated 2026-08-17
Weakness: CWE-863

Description

A flaw was found in libssh. On servers with GSSAPIKeyExchange enabled, the gssapi-keyex path does not verify whether the authenticated Kerberos principal is authorized for the requested local user, allowing authenticated clients to log in as arbitrary users.

Affected products

libssh: all versions
Red Hat Enterprise Linux: 10.0
RedHat Hardened Images: all versions

References

https://access.redhat.com/errata/RHSA-2026:42922
https://access.redhat.com/errata/RHSA-2026:55855
https://access.redhat.com/security/cve/CVE-2026-59851
https://bugzilla.redhat.com/show_bug.cgi?id=2498184

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