CVE-2025-26466 | Openssh: denial-of-service in 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.

Published: 2025-02-28 Last update: 2026-02-10 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-26466 is rated Moderate Risk (57.5/100): CVSS Medium severity, with high exploitation likelihood (EPSS 62.37%, 98th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-26466

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-08 62.87% 62.37% -0.51%
2 2026-04-21 60.43% 62.87% +2.44%
3 2026-03-29 — 60.43% —

Full EPSS history (43 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-26466

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 3.6 [email protected]
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 3.6 [email protected]

Weakness enumeration for CVE-2025-26466

OS Trackers for CVE-2025-26466

vendor priority summary link
alpine — CVE-2025-26466: 1 source package rows (openssh); 6 state rows across 5 repos (3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 6, open 0. https://security.alpinelinux.org/vuln/CVE-2025-26466
debian unimportant CVE-2025-26466 unimportant priority: Debian including 1 source packages (openssh), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2025-26466
gentoo normal CVE-2025-26466: 1 GLSA(s) (202502-01), 1 atom(s) (net-misc/openssh); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2025-26466
redhat medium — https://access.redhat.com/security/cve/CVE-2025-26466
suse medium CVE-2025-26466 severity moderate: SUSE including 84 source package names (15.7.20.5.1:openssh-9.6p1-150600.6.15.2, 15.7.20.5.1:openssh-clients-9.6p1-150600.6.15.2, …), 823 product×package rows across 183 product lines (Container suse/git, Container suse/hpc/warewulf4-x86_64/sle-hpc-node, … (183 product lines)): Fixed 683, Known Not Affected 140. https://www.suse.com/security/cve/CVE-2025-26466/
ubuntu medium CVE-2025-26466 medium priority: Ubuntu including 2 source packages (openssh, openssh-ssh1), 16 status rows across 9 suites (bionic, focal, jammy, noble, oracular, plucky, trusty, upstream, xenial): not-affected 11, released 3, ignored 1, needs-triage 1. https://ubuntu.com/security/CVE-2025-26466

Affected software / configurations for CVE-2025-26466

Vendor Product Version Raw CPE
openbsd openssh 9.5 cpe:2.3:a:openbsd:openssh:9.5:p1:*:*:*:*:*:*
openbsd openssh 9.6 cpe:2.3:a:openbsd:openssh:9.6:-:*:*:*:*:*:*
openbsd openssh 9.6 cpe:2.3:a:openbsd:openssh:9.6:p1:*:*:*:*:*:*
openbsd openssh 9.7 cpe:2.3:a:openbsd:openssh:9.7:-:*:*:*:*:*:*
openbsd openssh 9.7 cpe:2.3:a:openbsd:openssh:9.7:p1:*:*:*:*:*:*
openbsd openssh 9.8 cpe:2.3:a:openbsd:openssh:9.8:-:*:*:*:*:*:*
openbsd openssh 9.8 cpe:2.3:a:openbsd:openssh:9.8:p1:*:*:*:*:*:*
openbsd openssh 9.9 cpe:2.3:a:openbsd:openssh:9.9:-:*:*:*:*:*:*
openbsd openssh 9.9 cpe:2.3:a:openbsd:openssh:9.9:p1:*:*:*:*:*:*
canonical ubuntu_linux 24.04 cpe:2.3:o:canonical:ubuntu_linux:24.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 24.10 cpe:2.3:o:canonical:ubuntu_linux:24.10:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
debian debian_linux 12.0 cpe:2.3:o:debian:debian_linux:12.0:*:*:*:*:*:*:*
debian debian_linux 13.0 cpe:2.3:o:debian:debian_linux:13.0:*:*:*:*:*:*:*

References for CVE-2025-26466

URL Tags
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 List Third Party Advisory
https://www.openwall.com/lists/oss-security/2025/02/18/4 Mailing List Third 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
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