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

mediumCVSS 4.3CVE-2026-55653

CSIRTS triage

vendor: OpenSSH product: OpenSSH Denial of serviceaffected: Red Hat Enterprise Linux versions

What: This vulnerability involves a double free in OpenSSH leading to client-side denial of service.
Who is affected: Users of OpenSSH on Red Hat Enterprise Linux versions.
Urgency: Remediation is medium urgency due to the medium severity rating.
Action: Update OpenSSH to the latest version.

AI-assisted analysis generated from the source advisory — verify against the original.

⚡ Watch OpenSSH

Get an email when a new OpenSSH advisory drops — max one per day, one-click unsubscribe.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 4.3
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55653

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-556530.24% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 15% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-55653	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

medium[UPDATE] [medium] OpenSSH: Multiple vulnerabilitiescert-bund

Recent advisories for Openssh

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

medium[NEW] [medium] OpenSSH: Multiple vulnerabilitiescert-bund · 2026-07-10
medium[UPDATE] [medium] OpenSSH: Multiple vulnerabilitiescert-bund · 2026-07-09
highCVE-2026-47829: Argument Injection in bosh-cli allows a compromised BOSH Director to inject arbitrary OpenSSH …nvd · 2026-07-09
medium[UPDATE] [medium] OpenSSH: Multiple vulnerabilitiescert-bund · 2026-07-08
highCVE-2026-60002: ssh in OpenSSH before 10.4 can have a use-after-free when a server changes its host key during…nvd · 2026-07-08
mediumCVE-2026-60001: sshd in OpenSSH before 10.4 does not always honor the minimum authentication delay.nvd · 2026-07-08