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Fencer Vulns
medium 4.3

CVE-2026-55653 json

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

published 2026-06-23 4 mo ago modified 2026-11-05 3 d ago also EUVD-2026-38412

cvss
4.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 45%
public exploits
0
none known

Summary

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).

Patch / fix

  • Red Hat Red Hat Enterprise Linux 10 0:9.9p1-25.el10_2
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support 0:9.9p1-7.el10_0.5
  • Red Hat Red Hat Enterprise Linux 8 0:8.0p1-30.el8_10
  • Red Hat Red Hat Enterprise Linux 9 0:9.9p1-9.el9_8
  • Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions 0:8.7p1-30.el9_2.13
  • Red Hat Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions 0:8.7p1-38.el9_4.10
  • Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support 0:8.7p1-45.el9_6.5
  • Red Hat Red Hat Hardened Images 10.3p1-6.hum1
  • Red Hat Red Hat OpenShift AI 3.0 1791818496, 1791818502, 1791818505, 1791818589, 1791818590, 1793042072
  • Red Hat Red Hat OpenShift AI 3.2 1791818512, 1791818587, 1791818598, 1791818602, 1791818778
  • Red Hat Red Hat OpenShift AI 3.3 1791818627, 1791818662, 1791818782, 1791818790, 1791818792, 1791818874, 1791818877
  • Red Hat Red Hat OpenShift AI 3.4 1791881486, 1791881487, 1791881612, 1791881732, 1791881769, 1791883315, 1791883722, 1791885505, 1791885618
  • Red Hat Red Hat OpenShift AI 3.5 1791818749, 1791818901, 1791818979, 1791819104, 1791819123, 1791819206, 1791819252, 1791819495, 1791820333
  • Red Hat Red Hat Update Infrastructure 5 1786435483, 1786533529, 1787135742, 1787241260
  • openssh RHEL 10.2 9.9p1-25.el10_2
  • openssh-keycat RHEL 10.2 9.9p1-25.el10_2
  • openssh-server RHEL 10.2 9.9p1-25.el10_2
  • openssh-askpass RHEL 10.2 9.9p1-25.el10_2
  • openssh-clients RHEL 10.2 9.9p1-25.el10_2
  • openssh-keysign RHEL 10.2 9.9p1-25.el10_2
  • openssh RHEL 8 8.0p1-30.el8_10
  • openssh-cavs RHEL 8 8.0p1-30.el8_10

red hat advisories RHSA-2026:80513RHSA-2026:76993RHSA-2026:76748RHSA-2026:47757RHSA-2026:47755RHSA-2026:47756

  • openssh AlmaLinux 8 8.0p1-30.el8_10
  • openssh-cavs AlmaLinux 8 8.0p1-30.el8_10
  • openssh-ldap AlmaLinux 8 8.0p1-30.el8_10
  • openssh-keycat AlmaLinux 8 8.0p1-30.el8_10
  • openssh-server AlmaLinux 8 8.0p1-30.el8_10
  • openssh-askpass AlmaLinux 8 8.0p1-30.el8_10
  • openssh-clients AlmaLinux 8 8.0p1-30.el8_10
  • pam_ssh_agent_auth AlmaLinux 8 0.10.3-7.30.el8_10

almalinux advisories ALSA-2026:47755ALSA-2026:47756ALSA-2026:47757

  • openssh Rocky Linux 9 9.9p1-9.el9_8.rocky.0.1
  • openssh Rocky Linux 10 9.9p1-25.el10_2.rocky.0.1
  • openssh Rocky Linux 8 8.0p1-30.el8_10

rocky linux advisories RLSA-2026:47756RLSA-2026:47757RLSA-2026:47755

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-55653 updated cvss 4.3

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

  • Red Hat Enterprise Linux 6 openssh, openssh-ldap, openssh-server, openssh-askpass, openssh-clients, pam_ssh_agent_auth Red Hat Enterprise Linux 7 openssh, openssh-cavs, openssh-ldap, openssh-keycat, openssh-server, openssh-askpass, +3 more
    affected: workaround, no fix available
  • Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux AppStream (v. 8) openssh-askpass 8.0p1-30.el8_10
    fixed: vendor fix RHSA-2026:47755
  • Red Hat Enterprise Linux AppStream (v. 9) openssh-askpass 9.9p1-9.el9_8, pam_ssh_agent_auth 0.10.4-7.9.el9_8
    fixed: vendor fix RHSA-2026:47756
  • Red Hat Enterprise Linux AppStream (v. 10) openssh-askpass 9.9p1-25.el10_2, openssh-keysign 9.9p1-25.el10_2
    fixed: vendor fix RHSA-2026:47757
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) openssh-askpass 8.7p1-30.el9_2.13, pam_ssh_agent_auth 0.10.4-5.30.el9_2.13
    fixed: vendor fix RHSA-2026:89739
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) openssh-askpass 9.9p1-7.el10_0.5, openssh-keysign 9.9p1-7.el10_0.5
    fixed: vendor fix RHSA-2026:76748
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) openssh-askpass 8.7p1-45.el9_6.5, pam_ssh_agent_auth 0.10.4-5.45.el9_6.5
    fixed: vendor fix RHSA-2026:80513
show 15 more
  • Red Hat Enterprise Linux BaseOS (v. 8) openssh 8.0p1-30.el8_10, openssh-cavs 8.0p1-30.el8_10, openssh-ldap 8.0p1-30.el8_10, openssh-keycat 8.0p1-30.el8_10, openssh-server 8.0p1-30.el8_10, openssh-clients 8.0p1-30.el8_10, +1 more
    fixed: vendor fix RHSA-2026:47755
  • Red Hat Enterprise Linux BaseOS (v. 9) openssh 9.9p1-9.el9_8, openssh-keycat 9.9p1-9.el9_8, openssh-server 9.9p1-9.el9_8, openssh-clients 9.9p1-9.el9_8
    fixed: vendor fix RHSA-2026:47756
  • Red Hat Enterprise Linux BaseOS (v. 10) openssh 9.9p1-25.el10_2, openssh-keycat 9.9p1-25.el10_2, openssh-server 9.9p1-25.el10_2, openssh-clients 9.9p1-25.el10_2
    fixed: vendor fix RHSA-2026:47757
  • Red Hat Enterprise Linux BaseOS E4S (v.9.2) openssh 8.7p1-30.el9_2.13, openssh-keycat 8.7p1-30.el9_2.13, openssh-server 8.7p1-30.el9_2.13, openssh-clients 8.7p1-30.el9_2.13
    fixed: vendor fix RHSA-2026:89739
  • Red Hat Enterprise Linux BaseOS E4S (v.9.4) openssh-clients 8.7p1-38.el9_4.10
    fixed: vendor fix RHSA-2026:76993
  • Red Hat Enterprise Linux BaseOS EUS (v. 10.0) openssh 9.9p1-7.el10_0.5, openssh-keycat 9.9p1-7.el10_0.5, openssh-server 9.9p1-7.el10_0.5, openssh-clients 9.9p1-7.el10_0.5
    fixed: vendor fix RHSA-2026:76748
  • Red Hat Enterprise Linux BaseOS EUS (v.9.6) openssh 8.7p1-45.el9_6.5, openssh-keycat 8.7p1-45.el9_6.5, openssh-server 8.7p1-45.el9_6.5, openssh-clients 8.7p1-45.el9_6.5
    fixed: vendor fix RHSA-2026:80513
  • Red Hat Hardened Images openssh 10.3p1-6.hum1, openssh-keycat 10.3p1-6.hum1, openssh-server 10.3p1-6.hum1, openssh-askpass 10.3p1-6.hum1, openssh-clients 10.3p1-6.hum1, openssh-keysign 10.3p1-6.hum1, +1 more
    fixed: vendor fix RHSA-2026:36759
  • Red Hat OpenShift AI 3.0 rhai/base-image-cpu-rhel9 1791818589, rhai/base-image-cpu-rhel9 1793042072, rhai/base-image-tpu-rhel9 1791818496, rhai/base-image-cuda-rhel9 1791818590, rhai/base-image-rocm-rhel9 1791818502, rhai/base-image-spyre-rhel9 1791818505
    fixed: vendor fix RHSA-2026:91232
  • Red Hat OpenShift AI 3.2 rhai/base-image-cpu-rhel9 1791818598, rhai/base-image-tpu-rhel9 1791818512, rhai/base-image-cuda-rhel9 1791818587, rhai/base-image-rocm-rhel9 1791818512, rhai/base-image-rocm-rhel9 1791818778, rhai/base-image-spyre-rhel9 1791818602
    fixed: vendor fix RHSA-2026:82759
  • Red Hat OpenShift AI 3.3 rhai/base-image-cpu-rhel9 1791818874, rhai/base-image-tpu-rhel9 1791818782, rhai/base-image-spyre-rhel9 1791818877, rhai/base-image-neuron-rhel9 1791818792, rhai/base-image-rocm-6.4-rhel9 1791818782, rhai/base-image-rocm-7.0-rhel9 1791818790, +2 more
    fixed: vendor fix RHSA-2026:82902
  • Red Hat OpenShift AI 3.4 rhai/base-image-cpu-rhel9 1791885618, rhai/base-image-tpu-rhel9 1791881769, rhai/base-image-gaudi-rhel9 1791881486, rhai/base-image-spyre-rhel9 1791881732, rhai/base-image-neuron-rhel9 1791883722, rhai/base-image-rocm-6.4-rhel9 1791881487, +3 more
    fixed: vendor fix RHSA-2026:82753
  • Red Hat OpenShift AI 3.5 rhai/base-image-cpu-rhel9 1791819206, rhai/base-image-tpu-rhel9 1791818901, rhai/base-image-gaudi-rhel9 1791818749, rhai/base-image-rubin-rhel9 1791820333, rhai/base-image-spyre-rhel9 1791819252, rhai/base-image-neuron-rhel9 1791818979, +3 more
    fixed: vendor fix RHSA-2026:82908
  • Red Hat Update Infrastructure 5 rhui5/rhua-rhel9 1786533529, rhui5/rhua-tp-rhel9 1787241260, rhui5/installer-rhel9 1786435483, rhui5/installer-tp-rhel9 1787135742
    fixed: vendor fix RHSA-2026:54387
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) openssh-debuginfo 8.7p1-30.el9_2.13, pam_ssh_agent_auth-debuginfo 0.10.4-5.30.el9_2.13 Red Hat Enterprise Linux AppStream E4S (v.9.4) openssh-askpass 8.7p1-38.el9_4.10, pam_ssh_agent_auth 0.10.4-5.38.el9_4.10 Red Hat Enterprise Linux AppStream EUS (v. 10.0) openssh-debuginfo 9.9p1-7.el10_0.5, openssh-debugsource 9.9p1-7.el10_0.5, openssh-keycat-debuginfo 9.9p1-7.el10_0.5, openssh-server-debuginfo 9.9p1-7.el10_0.5, openssh-askpass-debuginfo 9.9p1-7.el10_0.5, openssh-clients-debuginfo 9.9p1-7.el10_0.5, +2 more Red Hat Enterprise Linux AppStream EUS (v.9.6) openssh-debuginfo 8.7p1-45.el9_6.5, openssh-debugsource 8.7p1-45.el9_6.5, openssh-keycat-debuginfo 8.7p1-45.el9_6.5, openssh-server-debuginfo 8.7p1-45.el9_6.5, openssh-askpass-debuginfo 8.7p1-45.el9_6.5, openssh-clients-debuginfo 8.7p1-45.el9_6.5, +2 more Red Hat Enterprise Linux BaseOS E4S (v.9.2) openssh-debuginfo 8.7p1-30.el9_2.13, pam_ssh_agent_auth-debuginfo 0.10.4-5.30.el9_2.13 Red Hat Enterprise Linux BaseOS E4S (v.9.4) openssh 8.7p1-38.el9_4.10, openssh-keycat 8.7p1-38.el9_4.10, openssh-server 8.7p1-38.el9_4.10
    +3 more products
    Red Hat Enterprise Linux BaseOS EUS (v. 10.0) openssh-debuginfo 9.9p1-7.el10_0.5, openssh-debugsource 9.9p1-7.el10_0.5, openssh-keycat-debuginfo 9.9p1-7.el10_0.5, openssh-server-debuginfo 9.9p1-7.el10_0.5, openssh-askpass-debuginfo 9.9p1-7.el10_0.5, openssh-clients-debuginfo 9.9p1-7.el10_0.5, +2 more Red Hat Enterprise Linux BaseOS EUS (v.9.6) openssh-debuginfo 8.7p1-45.el9_6.5, openssh-debugsource 8.7p1-45.el9_6.5, openssh-keycat-debuginfo 8.7p1-45.el9_6.5, openssh-server-debuginfo 8.7p1-45.el9_6.5, openssh-askpass-debuginfo 8.7p1-45.el9_6.5, openssh-clients-debuginfo 8.7p1-45.el9_6.5, +2 more Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1786533457, rhui5/cds-tp-rhel9 1787241206, rhui5/haproxy-rhel9 1786533449, rhui5/cds-kubernetes-rhel9 1786435241, rhui5/cds-kubernetes-tp-rhel9 1787241211
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.53% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugzilla.redhat.com https://bugzilla.redhat.com/show_bug.cgi?id=2462351 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Affected products

  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support
  • Red Hat Red Hat Hardened Images
  • Red Hat Red Hat OpenShift AI 3.0
  • Red Hat Red Hat OpenShift AI 3.2
  • Red Hat Red Hat OpenShift AI 3.3
  • Red Hat Red Hat OpenShift AI 3.4
  • Red Hat Red Hat OpenShift AI 3.5
  • Red Hat Red Hat Update Infrastructure 5
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat OpenShift Container Platform 4
  • Red Hat Red Hat OpenShift Container Platform 5

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.