Double Free in OpenBSD OpenSSH
CVE-2026-55653
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).
Vulnerability class: Double Free
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.005 (40.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 41st percentile — 40.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002
Affected products
- OpenBSD OpenSSH
- Red Hat Enterprise Linux 10 — versions 0:9.9p1-25.el10_2
- Red Hat Enterprise Linux 6
- Red Hat Enterprise Linux 7
- Red Hat Enterprise Linux 8 — versions 0:8.0p1-30.el8_10
- Red Hat Enterprise Linux 9 — versions 0:9.9p1-9.el9_8
- Red Hat Hardened Images — versions 10.3p1-6.hum1
- Red Hat Openshift Container Platform 4
- Red Hat Update Infrastructure 5 — versions 1786435483, 1786533529
- Red Hat Enterprise Linux — versions 6.0, 7.0, 8.0
Weakness classification (CWE)
References
- access.redhat.com/security/cve/CVE-2026-55653 (vdb-entry, Vendor Advisory)
- bugzilla.redhat.com/show_bug.cgi (issue-tracking, Exploit, Issue Tracking, Vendor Advisory)
- access.redhat.com/errata/RHSA-2026:36759 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:47755 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:47756 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:47757 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:54387 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:58981 (vendor-advisory)
Frequently asked questions
- What is CVE-2026-55653?
- CVE-2026-55653 is a medium-severity vulnerability in OpenBSD OpenSSH, classified under Double Free. CVSS score: 4.3/10. Published 2026-06-23.
- How severe is CVE-2026-55653?
- Medium severity. CVSS v3 base score is 4.3 out of 10.