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Vulnerability record · CVE-2026-55653 · published 23 June 2026

CVE-2026-55653: Openbsd openssh double free vulnerability

Openbsd · Openssh

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).

6.5 CVSS 3.1 Medium EPSS 0.51% · top 59.1% CWE-415 · Double free
6.5CVSS 3.1 base score
0.51%EPSS exploitation probability, 30 days
NoNot in CISA KEV
4Affected product versions listed by NVD
8References, 1 tagged exploit
1 Sep 2026Last modified by NVD

Description

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).

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Affected products

4 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://access.redhat.com/errata/RHSA-2026:36759
https://access.redhat.com/errata/RHSA-2026:47755
https://access.redhat.com/errata/RHSA-2026:47756
https://access.redhat.com/errata/RHSA-2026:47757
https://access.redhat.com/errata/RHSA-2026:54387
https://access.redhat.com/errata/RHSA-2026:58981
https://access.redhat.com/security/cve/CVE-2026-55653 Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2462351 ExploitIssue TrackingVendor Advisory

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Source: NIST National Vulnerability Database (record CVE-2026-55653), CISA KEV, FIRST EPSS (scores of 2026-09-29). This page is refreshed as NVD updates the record.