CVE Intelligence
Medium Memory corruption exploit reference

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

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).

Published Jun 23, 2026 · Updated Oct 14, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: redhat

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.6% (30-day exploitation probability)+7
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.6%
ahead of 47% of scored CVEs · Oct 14, 2026
Affects
Openbsd
Openssh and 18 more
CVSS base
6.5
Medium · 4 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Openbsd Openssh, Red Hat Enterprise Linux, Red Hat Hardened Images…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. Exploitation requires user interaction: tighten email/web filtering and warn affected users.
  5. Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Openbsd Openssh versions not specified by the source Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux version 7.0version 8.0version 9.0version 10.0version 6.0 Vulnerable NIST National Vulnerability Database
Red Hat Hardened Images versions not specified by the source Vulnerable NIST National Vulnerability Database
Red Hat Hardened Images versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Openshift Container Platform version 4.0 Vulnerable NIST National Vulnerability Database
Red Hat Red Hat Enterprise Linux 10 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Enterprise Linux 6 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Enterprise Linux 7 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Enterprise Linux 8 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Enterprise Linux 9 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat OpenShift AI 3.0 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat OpenShift AI 3.2 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat OpenShift AI 3.3 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat OpenShift AI 3.4 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat OpenShift AI 3.5 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat OpenShift Container Platform 4 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Red Hat Update Infrastructure 5 versions not specified by the source Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
6.5 CVSS 3.1 Medium 2.8 3.6 nvd@nist.gov via NIST National Vulnerability Database
4.3 CVSS 3.1 Medium 2.8 1.4 secalert@redhat.com via NIST National Vulnerability Database
4.3 CVSS 3.1 Medium — — GitHub, Inc. via GitHub Security Advisories
4.3 CVSS 3.1 Medium — — redhat via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)
Scoring entities (NIST, CNA, ADP) score independently; each score is shown with its origin. For prioritization we use 6.5 (NVD (NIST)) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-415 · Double Free

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.60%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products removed · 1
    Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
  • Affected products added · 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 ope
    Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
  • Affected products added · red hat/red hat openshift ai 3.4
    Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
  • Affected products added · red hat/red hat enterprise linux 10, red hat/red hat enterprise linux 10.0 extended update support, red hat/red hat ente
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • CVSS changed · 6.5
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVE published
    Jun 23, 2026 · redhat

Source activity

Repeated readings are counted rather than listed.

  • 3× References added · Oct 14, 2026 – Oct 14, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

50 on the record

Elsewhere on this site

Openbsd
every CVE for this vendor
Memory corruption
same class
CWE-415
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-92982 Ansible-operator-plugins: ansible operator plugins: arbitrary code execution via jinja2 template injection 6h
  • CVE-2026-110924 Openssh: openssh: gssapi delegated credentials can be stored after a failed authentication 8h
  • CVE-2026-110927 Openssh: openssh: a compressed payload can expand past the maximum packet size 8h
  • CVE-2026-110926 Openssh: openssh: shared lz77 compression dictionary leaks plaintext across channels 16h
  • CVE-2026-110923 Openssh: openssh: sftp can write outside the destination directory from a server-supplied path 16h
  • CVE-2026-110925 Openssh: openssh: '$' and '\' in a command-line username expand through %u 16h

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-55653 is "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", rated Medium. It affects Openssh (Openbsd); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.5 describes technical severity. EPSS 0.60% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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