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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 40.7% (30-day exploitation probability)+15
- Technical severity (medium)+3
- CISA SSVC: exploitation "poc"+5
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Canonical Ubuntu Linux, Debian Debian Linux, Openbsd Openssh…).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- EPSS ahead of 99% of scored CVEs: prioritize it in the patch queue.
- Search available logs for exploit probes matching the vulnerability class (denial of service), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Canonical | Ubuntu Linux | version 24.04version 24.10 | Vulnerable | NIST National Vulnerability Database |
| Debian | Debian Linux | version 11.0version 12.0version 13.0 | Vulnerable | NIST National Vulnerability Database |
| Openbsd | Openssh |
version 9.5-p1version 9.6version 9.6-p1version 9.7version 9.7-p1version 9.8version 9.8-p1version 9.9 and 1 moreversion 9.9-p1 |
Vulnerable | NIST National Vulnerability Database |
| Red Hat | Red Hat Enterprise Linux 10 | versions not specified by the source | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Red Hat | Red Hat Enterprise Linux 9 | versions not specified by the source | Vulnerable | CVE Program (cve.org) e CISA ADP |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 5.9 | CVSS 3.1 | Medium | 2.2 | 3.6 | secalert@redhat.com via NIST National Vulnerability Database |
| 5.9 | CVSS 3.1 | Medium | 2.2 | 3.6 | nvd@nist.gov via NIST National Vulnerability Database |
| 5.9 | CVSS 3.1 | Medium | — | — | redhat via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
CWE-770 · Allocation of Resources Without Limits or Throttling
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 40.65%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Track CPU/memory spikes and availability drops correlated with request patterns.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · red hat/red hat enterprise linux 10, red hat/red hat enterprise linux 9
- SSVC assessment updated
- Record published
- CVSS changed · 5.9
- Source status changed · → Modified
- Record created in this database
- 2025
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× References added · Oct 15, 2026 – Oct 15, 2026
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
18 on the record
- seclists.org/oss-sec/2025/q1/144
- access.redhat.com/errata/RHBA-2025:6305
- www.openwall.com/lists/oss-security/2025/02/18/4
- bugzilla.redhat.com/show_bug.cgi
- security.netapp.com/advisory/ntap-20250228-0002/
- seclists.org/fulldisclosure/2025/May/8
- www.openwall.com/lists/oss-security/2025/02/18/1
- seclists.org/fulldisclosure/2025/May/7
- www.qualys.com/2025/02/18/openssh-mitm-dos.txt
- seclists.org/fulldisclosure/2025/Feb/18
- www.vicarius.io/vsociety/posts/cve-2025-26466-detection-script-memory-consumption-vul
- access.redhat.com/security/cve/CVE-2025-26466
- www.vicarius.io/vsociety/posts/cve-2025-26466-mitigation-script-memory-consumption-vu
- bugzilla.suse.com/show_bug.cgi
- security-tracker.debian.org/tracker/CVE-2025-26466
- cert-portal.siemens.com/productcert/html/ssa-398330.html
- ubuntu.com/security/CVE-2025-26466
- access.redhat.com/errata/RHSA-2025:6993
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-110924 Openssh: openssh: gssapi delegated credentials can be stored after a failed authentication 7h
- Medium CVE-2026-110927 Openssh: openssh: a compressed payload can expand past the maximum packet size 7h
- Medium CVE-2026-110926 Openssh: openssh: shared lz77 compression dictionary leaks plaintext across channels 15h
- Medium CVE-2026-110925 Openssh: openssh: '$' and '\' in a command-line username expand through %u 15h
- Medium CVE-2026-110923 Openssh: openssh: sftp can write outside the destination directory from a server-supplied path 15h
- Medium CVE-2026-86856 Dpdk: dpdk: stack and heap buffer overflow in nfp vdpa driver 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2025-26466 is "Openssh: denial-of-service in openssh", rated Medium. It affects Ubuntu Linux (Canonical); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.9 describes technical severity. EPSS 40.65% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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