OpenSSH DH-GEX Double Free DoS in FIPS Mode
CVE-2026-55653 Published on June 23, 2026

Openssh: double free in red hat enterprise linux versions of openssh dh-gex client path during fips known-group validation leads to client-side denial of service
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).

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Vulnerability Analysis

CVE-2026-55653 can be exploited with network access, requires user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a small impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
REQUIRED
Scope:
UNCHANGED
Confidentiality Impact:
NONE
Integrity Impact:
NONE
Availability Impact:
LOW

Timeline

Reported to Red Hat.

Made public. 57 days later.

Weakness Type

What is a Double-free Vulnerability?

The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations. When a program calls free() twice with the same argument, the program's memory management data structures become corrupted. This corruption can cause the program to crash or, in some circumstances, cause two later calls to malloc() to return the same pointer. If malloc() returns the same value twice and the program later gives the attacker control over the data that is written into this doubly-allocated memory, the program becomes vulnerable to a buffer overflow attack.

CVE-2026-55653 has been classified to as a Double-free vulnerability or weakness.


Products Associated with CVE-2026-55653

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Red Hat Enterprise Linux (RHEL)
 
Red Hat Hummingbird
 
Red Hat Openshift
 
Red Hat Rhui
 
Red Hat Enterprise Linux Eus
 
Red Hat Rhel E4s
 
Red Hat Rhel Eus
 
Red Hat Openshift Ai
 

Affected Versions

Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 10.0 Extended Update Support: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions: Red Hat Enterprise Linux 9.6 Extended Update Support: Red Hat Hardened Images: Red Hat OpenShift AI 3.0: Red Hat OpenShift AI 3.0: Red Hat OpenShift AI 3.0: Red Hat OpenShift AI 3.0: Red Hat OpenShift AI 3.0: Red Hat OpenShift AI 3.2: Red Hat OpenShift AI 3.2: Red Hat OpenShift AI 3.2: Red Hat OpenShift AI 3.2: Red Hat OpenShift AI 3.2: Red Hat OpenShift AI 3.2: Red Hat OpenShift AI 3.3: Red Hat OpenShift AI 3.3: Red Hat OpenShift AI 3.3: Red Hat OpenShift AI 3.3: Red Hat OpenShift AI 3.3: Red Hat OpenShift AI 3.3: Red Hat OpenShift AI 3.3: Red Hat OpenShift AI 3.3: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.4: Red Hat OpenShift AI 3.5: Red Hat OpenShift AI 3.5: Red Hat OpenShift AI 3.5: Red Hat OpenShift AI 3.5: Red Hat OpenShift AI 3.5: Red Hat OpenShift AI 3.5: Red Hat OpenShift AI 3.5: Red Hat OpenShift AI 3.5: Red Hat OpenShift AI 3.5: Red Hat Update Infrastructure 5: Red Hat Update Infrastructure 5: Red Hat Update Infrastructure 5: Red Hat Update Infrastructure 5: Red Hat Enterprise Linux 6: Red Hat Enterprise Linux 7: Red Hat OpenShift Container Platform 4: Red Hat OpenShift Container Platform 4:

Exploit Probability

EPSS
0.25%
Percentile
16.23%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.