CVE-2026-55653 Memory corruption in Red Hat Enterprise Linux 10
A malicious SSH server can cause a client-side denial of service via a double free in OpenSSH during FIPS mode DH-GEX validation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-55653?
CVE-2026-55653 is a medium-severity memory corruption vulnerability in OpenSSH, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
A flaw was found in OpenSSH. A malicious SSH server can exploit a double free vulnerability in the Diffie-Hellman Group Exchange (DH-GEX) client path. This occurs during FIPS (Federal Information Processing Standards) mode known-group validation when the client processes attacker-controlled DH-GEX group parameters. Successful exploitation leads to client-side process termination, resulting in a Denial of Service (DoS).
Weakness: CWE-415
Which versions are affected by CVE-2026-55653?
It affects 4 products.
Products include OpenSSH, Redhat Enterprise Linux, Redhat Hardened Images, Redhat Openshift Container Platform.
How do I fix CVE-2026-55653?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-55653 being exploited?
There is no known exploitation of CVE-2026-55653 in the wild and no public exploit code.
Other vulnerabilities in OpenSSH
Sources
Also known as AZL-91200, CLSA-2026-1783694178, CLSA-2026-1783706054, ECHO-bc9c-5617-0a3c, GHSA-28f3-55mq-pp68, UBUNTU-CVE-2026-55653.