CVE-2026-59849 Libssh: libssh: denial of service via automatic certificate authentication loop

What is CVE-2026-59849?

CVE-2026-59849 is a low-severity denial of service 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. Logic errors in automatic certificate-based public key authentication can cause libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected by a server, leading to denial of service.

Weakness: CWE-835

Which versions are affected by CVE-2026-59849?

It affects 11 products.

Products include Libssh Libssh, Redhat Enterprise Linux, Redhat Enterprise Linux for Els, Redhat Enterprise Linux for Eus, Redhat Enterprise Linux for Ibm Z Systems, Redhat Enterprise Linux for Ibm Z Systems Els and 5 more.

How do I fix CVE-2026-59849?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-59849 being exploited?

There is no known exploitation of CVE-2026-59849 in the wild and no public exploit code.

Other vulnerabilities in Redhat Enterprise Linux

• CVE-2026-59851 Libssh: libssh: authentication bypass via missing gssapi principal check High 8.8
• CVE-2025-5987 Libssh: invalid return code for chacha20 poly1305 with openssl backend High 8.1
• CVE-2025-14821 Libssh: libssh: insecure default configuration leads to local man-in-the-middle attacks on windows High 7.8
• CVE-2012-4560 Memory corruption in n/a High 7.5
• CVE-2012-4562 Integer overflow in n/a High 7.5

All Redhat Enterprise Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2026-59849, DEBIAN-CVE-2026-59849, ECHO-273b-69ec-2249, GHSA-jp6g-7mqj-wj53, MINI-w34c-q7f4-m4q9, UBUNTU-CVE-2026-59849.