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Vulnerability · Published Jun 23, 2026 · Assigned by redhat

CVE-2026-55653Openssh: 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

Medium 4.3

In plain English

A medium-severity double free in Red Hat Enterprise Linux 10 from Red Hat. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)0.5%top 55.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

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).

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
AlmaLinux:10openssh9.9p1-25.el10_2.alma.1ALSA-2026:47757
AlmaLinux:8openssh8.0p1-30.el8_10ALSA-2026:47755
AlmaLinux:9openssh9.9p1-9.el9_8.alma.1ALSA-2026:47756
AlmaLinux:10openssh-askpass9.9p1-25.el10_2.alma.1ALSA-2026:47757
AlmaLinux:8openssh-askpass8.0p1-30.el8_10ALSA-2026:47755
AlmaLinux:9openssh-askpass9.9p1-9.el9_8.alma.1ALSA-2026:47756
AlmaLinux:8openssh-cavs8.0p1-30.el8_10ALSA-2026:47755
AlmaLinux:10openssh-clients9.9p1-25.el10_2.alma.1ALSA-2026:47757
AlmaLinux:8openssh-clients8.0p1-30.el8_10ALSA-2026:47755
AlmaLinux:9openssh-clients9.9p1-9.el9_8.alma.1ALSA-2026:47756
AlmaLinux:10openssh-keycat9.9p1-25.el10_2.alma.1ALSA-2026:47757
AlmaLinux:8openssh-keycat8.0p1-30.el8_10ALSA-2026:47755
AlmaLinux:9openssh-keycat9.9p1-9.el9_8.alma.1ALSA-2026:47756
AlmaLinux:10openssh-keysign9.9p1-25.el10_2.alma.1ALSA-2026:47757
AlmaLinux:8openssh-ldap8.0p1-30.el8_10ALSA-2026:47755
AlmaLinux:10openssh-server9.9p1-25.el10_2.alma.1ALSA-2026:47757
AlmaLinux:8openssh-server8.0p1-30.el8_10ALSA-2026:47755
AlmaLinux:9openssh-server9.9p1-9.el9_8.alma.1ALSA-2026:47756
AlmaLinux:8pam_ssh_agent_auth0.10.3-7.30.el8_10ALSA-2026:47755
AlmaLinux:9pam_ssh_agent_auth0.10.4-7.9.el9_8.alma.1ALSA-2026:47756
Debian:12opensshno fix listedDEBIAN-CVE-2026-55653
Debian:13opensshno fix listedDEBIAN-CVE-2026-55653
Debian:14opensshno fix listedDEBIAN-CVE-2026-55653
Rocky Linux:10openssh0:9.9p1-25.el10_2.rocky.0.1RLSA-2026:47757
Rocky Linux:8openssh0:8.0p1-30.el8_10RLSA-2026:47755
Rocky Linux:9openssh0:9.9p1-9.el9_8.rocky.0.1RLSA-2026:47756
Ubuntu:22.04:LTSopenssh-ssh1no fix listedUBUNTU-CVE-2026-55653
Ubuntu:24.04:LTSopenssh-ssh1no fix listedUBUNTU-CVE-2026-55653
Ubuntu:25.10openssh-ssh1no fix listedUBUNTU-CVE-2026-55653
Ubuntu:26.04:LTSopenssh-ssh1no fix listedUBUNTU-CVE-2026-55653
Ubuntu:26.10openssh-ssh1no fix listedUBUNTU-CVE-2026-55653

Affected products (as reported)

VendorProductVersions
Red Hat Red Hat Enterprise Linux 10 see references
Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support see references
Red Hat Red Hat Enterprise Linux 8 see references
Red Hat Red Hat Enterprise Linux 8 see references
Red Hat Red Hat Enterprise Linux 9 see references
Red Hat Red Hat Enterprise Linux 9 see references
Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions see references
Red Hat Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions see references
Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support see references
Red Hat Red Hat Hardened Images see references
Red Hat Red Hat OpenShift AI 3.0 see references
Red Hat Red Hat OpenShift AI 3.0 see references
Red Hat Red Hat OpenShift AI 3.0 see references
Red Hat Red Hat OpenShift AI 3.0 see references
Red Hat Red Hat OpenShift AI 3.0 see references
Red Hat Red Hat OpenShift AI 3.0 see references
Red Hat Red Hat OpenShift AI 3.2 see references
Red Hat Red Hat OpenShift AI 3.2 see references
Red Hat Red Hat OpenShift AI 3.2 see references
Red Hat Red Hat OpenShift AI 3.2 see references
Red Hat Red Hat OpenShift AI 3.2 see references
Red Hat Red Hat OpenShift AI 3.2 see references
Red Hat Red Hat OpenShift AI 3.3 see references
Red Hat Red Hat OpenShift AI 3.3 see references
Red Hat Red Hat OpenShift AI 3.3 see references
Red Hat Red Hat OpenShift AI 3.3 see references
Red Hat Red Hat OpenShift AI 3.3 see references
Red Hat Red Hat OpenShift AI 3.3 see references
Red Hat Red Hat OpenShift AI 3.3 see references
Red Hat Red Hat OpenShift AI 3.3 see references

Weakness: CWE-415 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

References