CVE-2026-55653: openbsd openssh Double Free
Vulnerability summary
CVE-2026-55653 is a medium (CVSS 6.5) Double Free vulnerability in openbsd openssh. EPSS estimates a 0.73% chance of exploitation in the next 30 days, higher than 53.4% of scored vulnerabilities. 1 public exploit is recorded.
Advisory lineage
Upstream 0 · Downstream 7Timeline
- 23-06-2026PublishedVulnerability first disclosed.
- 14-10-2026Last modifiedVulnerability information updated.
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 metrics
4 scores · 4 sources · 1 version- CVE.orgCNA4.3MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:LDiffers
- OSV · UbuntuEcosystem advisory · calculated6.5MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated4.3MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:LDiffers
EPSS trend
Probability
0.73%
Chance of exploitation in the next 30 days
Percentile
53%
Versus all other CVEs
30-day change
+0.43 pp
From 0.30% on 18-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
1 foundExploit Reference (bugzilla.redhat.com)
Maturity: unknown
Weaknesses
CWE · root causeAffected systems
Redhat3 products
- enterprise_linuxEOL6.0 | 7.0 | 8.0 | 9.0 | 10.0
- hardened_imagesna
- openshift_container_platform4.0
Ubuntu2 products
- opensshAll versions (No fix recorded)
- openssh-ssh1All versions (No fix recorded)
Debian1 product
- opensshAll versions (No fix recorded)
Openbsd1 product
- opensshna
4 vendors · 7 products
