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Vulnerability record · CVE-2025-26466 · published 28 February 2025

CVE-2025-26466: Openbsd openssh allocation without limits vulnerability

Openbsd · Openssh

A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack.

5.9 CVSS 3.1 Medium EPSS 40% · top 1.4% CWE-770 · Allocation without limits
5.9CVSS 3.1 base score
40%EPSS exploitation probability, 30 days
NoNot in CISA KEV
3Affected product versions listed by NVD
16References
30 Jun 2026Last modified by NVD

Description

A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack.

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

Affected products

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

References

LinkTags
https://access.redhat.com/security/cve/CVE-2025-26466 Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2345043 Issue Tracking
https://seclists.org/oss-sec/2025/q1/144
https://www.qualys.com/2025/02/18/openssh-mitm-dos.txt Third Party Advisory
http://seclists.org/fulldisclosure/2025/Feb/18
http://seclists.org/fulldisclosure/2025/May/7
http://seclists.org/fulldisclosure/2025/May/8
https://bugzilla.suse.com/show_bug.cgi?id=1237041 Third Party Advisory
https://security-tracker.debian.org/tracker/CVE-2025-26466 Third Party Advisory
https://security.netapp.com/advisory/ntap-20250228-0002/ Third Party Advisory
https://ubuntu.com/security/CVE-2025-26466 Third Party Advisory
https://www.openwall.com/lists/oss-security/2025/02/18/1 Mailing ListThird Party Advisory
https://www.openwall.com/lists/oss-security/2025/02/18/4 Mailing ListThird Party Advisory
https://www.vicarius.io/vsociety/posts/cve-2025-26466-detection-script-memory-consumption-vulnerability-in-openssh
https://www.vicarius.io/vsociety/posts/cve-2025-26466-mitigation-script-memory-consumption-vulnerability-in-openssh
https://www.qualys.com/2025/02/18/openssh-mitm-dos.txt Third Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2025-26466), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.