CVE-2026-59851 Libssh: libssh: authentication bypass via missing gssapi principal check
Attackers can bypass authentication to log in as arbitrary users on servers using GSSAPI key exchange without proper principal verification.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-59851?
CVE-2026-59851 is a high-severity authentication bypass vulnerability in Redhat Enterprise Linux, published on 21 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Weakness: CWE-863
Which versions are affected by CVE-2026-59851?
It affects 3 products.
Products include Libssh Libssh, Redhat Enterprise Linux, Redhat Hardened Images.
How do I fix CVE-2026-59851?
Apply the vendor's patch.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-59851 being exploited?
There is no known exploitation of CVE-2026-59851 in the wild and no public exploit code.
Other vulnerabilities in Redhat Enterprise Linux
- CVE-2025-5987 Libssh: invalid return code for chacha20 poly1305 with openssl backend
- CVE-2025-14821 Libssh: libssh: insecure default configuration leads to local man-in-the-middle attacks on windows
- CVE-2012-4560 Memory corruption in n/a
- CVE-2012-4562 Integer overflow in n/a
- CVE-2012-6063 Use after free in n/a
Sources
Also known as BELL-CVE-2026-59851, DEBIAN-CVE-2026-59851, GHSA-x5cr-v39m-53gw.