CVE-2025-26466

Openssh: denial-of-service in openssh

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.

Remediation

Workaround:

  • 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.

Category

5.9
CVSS
Severity: Medium
CVSS 3.1 •
EPSS 46.45% Top 5%
Third-Party Advisory redhat.com Third-Party Advisory qualys.com Third-Party Advisory suse.com Third-Party Advisory debian.org Third-Party Advisory netapp.com Third-Party Advisory ubuntu.com Third-Party Advisory openwall.com Third-Party Advisory openwall.com
Affected: Red Hat Red Hat Enterprise Linux 10
Affected: Red Hat Red Hat Enterprise Linux 6
Affected: Red Hat Red Hat Enterprise Linux 7
Affected: Red Hat Red Hat Enterprise Linux 8
Affected: Red Hat Red Hat Enterprise Linux 9
Affected: Red Hat Red Hat OpenShift Container Platform 4
Published at:
Updated at:

References

Link Tags
https://access.redhat.com/security/cve/CVE-2025-26466 vdb entry 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
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

Frequently Asked Questions

What is the severity of CVE-2025-26466?
CVE-2025-26466 has been scored as a medium severity vulnerability.
How to fix CVE-2025-26466?
As a workaround for remediating CVE-2025-26466: 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.
Is CVE-2025-26466 being actively exploited in the wild?
It is possible that CVE-2025-26466 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~46% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2025-26466?
CVE-2025-26466 affects Red Hat Red Hat Enterprise Linux 10, Red Hat Red Hat Enterprise Linux 6, Red Hat Red Hat Enterprise Linux 7, Red Hat Red Hat Enterprise Linux 8, Red Hat Red Hat Enterprise Linux 9, Red Hat Red Hat OpenShift Container Platform 4.
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