Openssh: denial-of-service in openssh
Summary
| CVE | CVE-2025-26466 |
|---|---|
| State | PUBLISHED |
| Assigner | redhat |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2025-02-28 22:15:40 UTC |
| Updated | 2026-06-30 01:16:23 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.1 5.9 MEDIUM from [email protected]
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS: 0.384740000 probability, percentile 0.983900000 (date 2026-07-01)
Problem Types: CWE-770 | CWE-770 Allocation of Resources Without Limits or Throttling
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Primary | 5.9 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | [email protected] | Secondary | 5.9 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | CNA | CVSS | 5.9 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
HighPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD Known Affected Configurations (CPE 2.3)
| Type | Vendor | Product | Version | Update | Edition | Language |
|---|---|---|---|---|---|---|
| Operating System | Canonical | Ubuntu Linux | 24.04 | All | All | All |
| Operating System | Canonical | Ubuntu Linux | 24.10 | All | All | All |
| Operating System | Debian | Debian Linux | 11.0 | All | All | All |
| Operating System | Debian | Debian Linux | 12.0 | All | All | All |
| Operating System | Debian | Debian Linux | 13.0 | All | All | All |
| Application | Openbsd | Openssh | 9.5 | p1 | All | All |
| Application | Openbsd | Openssh | 9.6 | - | All | All |
| Application | Openbsd | Openssh | 9.6 | p1 | All | All |
| Application | Openbsd | Openssh | 9.7 | - | All | All |
| Application | Openbsd | Openssh | 9.7 | p1 | All | All |
| Application | Openbsd | Openssh | 9.8 | - | All | All |
| Application | Openbsd | Openssh | 9.8 | p1 | All | All |
| Application | Openbsd | Openssh | 9.9 | - | All | All |
| Application | Openbsd | Openssh | 9.9 | p1 | All | All |
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Red Hat | Red Hat Enterprise Linux 10 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Enterprise Linux 6 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Enterprise Linux 7 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Enterprise Linux 8 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Enterprise Linux 9 | Not specified | Not specified |
| CNA | Red Hat | Red Hat OpenShift Container Platform 4 | Not specified | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| www.openwall.com/lists/oss-security/2025/02/18/1 | af854a3a-2127-422b-91ae-364da2661108 | www.openwall.com | Mailing List, Third Party Advisory |
| www.vicarius.io/vsociety/posts/cve-2025-26466-detection-script-memory-consump... | af854a3a-2127-422b-91ae-364da2661108 | www.vicarius.io | |
| seclists.org/fulldisclosure/2025/May/7 | af854a3a-2127-422b-91ae-364da2661108 | seclists.org | |
| ubuntu.com/security/CVE-2025-26466 | af854a3a-2127-422b-91ae-364da2661108 | ubuntu.com | Third Party Advisory |
| bugzilla.suse.com/show_bug.cgi | af854a3a-2127-422b-91ae-364da2661108 | bugzilla.suse.com | Third Party Advisory |
| seclists.org/oss-sec/2025/q1/144 | [email protected] | seclists.org | |
| www.openwall.com/lists/oss-security/2025/02/18/4 | af854a3a-2127-422b-91ae-364da2661108 | www.openwall.com | Mailing List, Third Party Advisory |
| access.redhat.com/security/cve/CVE-2025-26466 | [email protected] | access.redhat.com | Third Party Advisory |
| bugzilla.redhat.com/show_bug.cgi | [email protected] | bugzilla.redhat.com | Issue Tracking |
| seclists.org/fulldisclosure/2025/May/8 | af854a3a-2127-422b-91ae-364da2661108 | seclists.org | |
| security-tracker.debian.org/tracker/CVE-2025-26466 | af854a3a-2127-422b-91ae-364da2661108 | security-tracker.debian.org | Third Party Advisory |
| www.qualys.com/2025/02/18/openssh-mitm-dos.txt | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | www.qualys.com | Third Party Advisory |
| www.vicarius.io/vsociety/posts/cve-2025-26466-mitigation-script-memory-consum... | af854a3a-2127-422b-91ae-364da2661108 | www.vicarius.io | |
| seclists.org/fulldisclosure/2025/Feb/18 | af854a3a-2127-422b-91ae-364da2661108 | seclists.org | |
| security.netapp.com/advisory/ntap-20250228-0002 | af854a3a-2127-422b-91ae-364da2661108 | security.netapp.com | Third Party Advisory |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| CNA | 2025-02-11T19:51:30.375Z | Reported to Red Hat. |
| CNA | 2025-02-18T00:00:00.000Z | Made public. |
Workarounds
CNA: This issue can be mitigated by setting the following three different options in the sshd configuration file located at: /etc/ssh/sshd_config MaxStartups: Set to a reasonable value, this option controls the maximum number of concurrent unauthenticated connections the SSH server accepts; PerSourcePenalties: Set its suboptions to a reasonable value, this option is used to help sshd to detect and drop connections that are potentially malicious for the SSH server; LoginGraceTime: Set to a resonable value, this option controls how much time the SSH server will wait the client to authenticate before dropping its connection; All the three option above needs to be set to implement a full mitigation for this vulnerability.
There are currently no legacy QID mappings associated with this CVE.