CVE-2026-59843 Libssh: libssh: denial of service via zero advertised channel packet size
A remote authenticated peer can cause a denial of service in libssh by advertising a zero maximum packet size, leading to an infinite loop and CPU exhaustion.
- 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-2026-59843?
CVE-2026-59843 is a medium-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. A remote authenticated peer can advertise a zero maximum packet size in SSH_MSG_CHANNEL_OPEN, causing later channel writes to loop indefinitely and consume CPU, leading to denial of service.
Which versions are affected by CVE-2026-59843?
It affects 3 products.
Products include Libssh Libssh, Redhat Enterprise Linux, Redhat Hardened Images.
How do I fix CVE-2026-59843?
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-2026-59843 being exploited?
There is no known exploitation of CVE-2026-59843 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
- 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
Sources
Also known as AZL-93243, BELL-CVE-2026-59843, DEBIAN-CVE-2026-59843, ECHO-41e0-1521-8b3d, GHSA-4846-7xwg-pw5m, UBUNTU-CVE-2026-59843.