# CVE-2026-55653: 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

Status: published. Published: 2026-06-23. Updated: 2026-11-05.

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).

## Remediation

- workaround: To mitigate this issue, OpenSSH clients operating in FIPS mode should avoid negotiating the `diffie-hellman-group-exchange-sha256` key exchange algorithm. This can be achieved by explicitly listing allowed key exchange algorithms in the client's SSH configuration file (e.g., `/etc/ssh/ssh_config` or `~/.ssh/config`), ensuring `diffie-hellman-group-exchange-sha256` is *not* included. For example, to use a subset of common algorithms, you might configure:

```
KexAlgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group14-sha1
```

(Note: The above example `KexAlgorithms` list is illustrative and should be adjusted based on your environment's security requirements.)

Additionally, avoid using non-fatal client flows, such as `ssh-keyscan`, against untrusted SSH servers while FIPS mode is enabled. Changes to `ssh_config` will take effect for new SSH connections. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (openssh): ≥ 0:9.9p1-25.el10_2; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10.0 Extended Update Support (openssh): ≥ 0:9.9p1-7.el10_0.5; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (openssh): ≥ 0:8.0p1-30.el8_10; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (openssh): ≥ 0:9.9p1-9.el9_8; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions (openssh): ≥ 0:8.7p1-30.el9_2.13; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions (openssh): ≥ 0:8.7p1-38.el9_4.10; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9.6 Extended Update Support (openssh): ≥ 0:8.7p1-45.el9_6.5; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Hardened Images (openssh-main): ≥ 10.3p1-6.hum1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.0 (rhai/base-image-cuda-rhel9): ≥ 1791818590; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.0 (rhai/base-image-cpu-rhel9): ≥ 1791818589; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.0 (rhai/base-image-spyre-rhel9): ≥ 1791818505; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.0 (rhai/base-image-tpu-rhel9): ≥ 1791818496; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.0 (rhai/base-image-rocm-rhel9): ≥ 1791818502; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.0 (rhai/base-image-cpu-rhel9): ≥ 1793042072; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.2 (rhai/base-image-spyre-rhel9): ≥ 1791818602; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.2 (rhai/base-image-cpu-rhel9): ≥ 1791818598; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.2 (rhai/base-image-tpu-rhel9): ≥ 1791818512; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.2 (rhai/base-image-cuda-rhel9): ≥ 1791818587; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.2 (rhai/base-image-rocm-rhel9): ≥ 1791818778; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.2 (rhai/base-image-rocm-rhel9): ≥ 1791818512; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.3 (rhai/base-image-tpu-rhel9): ≥ 1791818782; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.3 (rhai/base-image-rocm-6.4-rhel9): ≥ 1791818782; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.3 (rhai/base-image-cuda-12.9-rhel9): ≥ 1791818627; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.3 (rhai/base-image-rocm-7.0-rhel9): ≥ 1791818790; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.3 (rhai/base-image-cpu-rhel9): ≥ 1791818874; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.3 (rhai/base-image-neuron-rhel9): ≥ 1791818792; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.3 (rhai/base-image-cuda-13.0-rhel9): ≥ 1791818662; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.3 (rhai/base-image-spyre-rhel9): ≥ 1791818877; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-neuron-rhel9): ≥ 1791883722; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-cuda-12.9-rhel9): ≥ 1791881612; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-cpu-rhel9): ≥ 1791885618; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-rocm-6.4-rhel9): ≥ 1791881487; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-spyre-rhel9): ≥ 1791881732; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-rocm-7.1-rhel9): ≥ 1791883315; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-gaudi-rhel9): ≥ 1791881486; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-tpu-rhel9): ≥ 1791881769; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-cuda-13.0-rhel9): ≥ 1791885505; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-spyre-rhel9): ≥ 1791819252; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-gaudi-rhel9): ≥ 1791818749; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-cpu-rhel9): ≥ 1791819206; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-neuron-rhel9): ≥ 1791818979; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-rocm-7.14-rhel9): ≥ 1791819123; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-tpu-rhel9): ≥ 1791818901; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-rubin-rhel9): ≥ 1791820333; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-cuda-13.0-rhel9): ≥ 1791819495; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.5 (rhai/base-image-cuda-12.9-rhel9): ≥ 1791819104; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/installer-rhel9): ≥ 1786435483; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/rhua-rhel9): ≥ 1786533529; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/installer-tp-rhel9): ≥ 1787135742; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/rhua-tp-rhel9): ≥ 1787241260; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (openssh): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (openssh): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 5 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 4.3 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.53% as of 2026-11-05; percentile 44.95%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-415

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/errata/RHSA-2026:36759 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:47755 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:47756 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:47757 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:54387 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:58981 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:76748 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:76993 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:80513 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82749 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82750 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82751 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82752 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82753 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82754 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82755 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82756 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82757 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82758 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82759 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82761 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82762 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82763 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82897 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82898 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82899 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82900 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82901 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82902 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82903 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82904 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82907 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82908 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82909 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82910 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82912 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82913 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82914 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82915 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82916 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82917 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82918 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82920 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82921 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82922 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82923 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:89739 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:91232 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-55653 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2462351 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-55653; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-55653; retrieved 2026-11-05; source updated Not reported

Revision: 1f56b3f986e26f83f94f64a57e0373d099af4d315dd0988274aeeea51c432917

Canonical: https://y2.dev/cve/CVE-2026-55653

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