CVE-2025-26466: Openssh: denial-of-service in openssh
First published: Tue Feb 11 2025(Updated: )
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.
Credit: secalert@redhat.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| OpenSSH | =9.5-p1 | |
| OpenSSH | =9.6 | |
| OpenSSH | =9.6-p1 | |
| OpenSSH | =9.7 | |
| OpenSSH | =9.7-p1 | |
| OpenSSH | =9.8 | |
| OpenSSH | =9.8-p1 | |
| OpenSSH | =9.9 | |
| OpenSSH | =9.9-p1 | |
| Ubuntu | =24.04 | |
| Ubuntu | =24.10 | |
| Debian | =11.0 | |
| Debian | =12.0 | |
| Debian | =13.0 | |
| debian/openssh | 1:8.4p1-5+deb11u3 1:8.4p1-5+deb11u4 1:9.2p1-2+deb12u5 1:9.9p2-1 |
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Reference Links
- https://www.theregister.com/2025/02/18/openssh_vulnerabilities_mitm_dos/
- https://www.bleepingcomputer.com/news/security/new-openssh-flaws-expose-ssh-servers-to-mitm-and-dos-attacks/
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-26466
- https://nvd.nist.gov/vuln/detail/CVE-2025-26466
- https://launchpad.net/bugs/cve/CVE-2025-26466
- https://security-tracker.debian.org/tracker/CVE-2025-26466
- https://ubuntu.com/security/CVE-2025-26466
- https://seclists.org/oss-sec/2025/q1/144
- https://bugzilla.redhat.com/show_bug.cgi?id=2345043
- https://access.redhat.com/security/cve/CVE-2025-26466
- https://www.qualys.com/2025/02/18/openssh-mitm-dos.txt
- https://security.netapp.com/advisory/ntap-20250228-0002/
- https://www.openssh.com/releasenotes.html#9.9p2
- https://github.com/openssh/openssh-portable/commit/dce6d80d2ed3cad2c516082682d5f6ca877ef714
- https://github.com/openssh/openssh-portable/commit/6ce00f0c2ecbb9f75023dbe627ee6460bcec78c2
- https://bugzilla.suse.com/show_bug.cgi?id=1237041
- https://www.openwall.com/lists/oss-security/2025/02/18/1
- https://www.openwall.com/lists/oss-security/2025/02/18/4
Frequently Asked Questions
What is the severity of CVE-2025-26466?
CVE-2025-26466 is classified as a Denial of Service vulnerability due to asymmetric resource consumption affecting memory and CPU.
How do I fix CVE-2025-26466?
To mitigate CVE-2025-26466, update to versions 1:9.9p1-3 or later of the OpenSSH package.
Which versions of OpenSSH are affected by CVE-2025-26466?
CVE-2025-26466 affects OpenSSH versions up to and including 1:9.9p1-3.
Can CVE-2025-26466 be exploited remotely?
Yes, CVE-2025-26466 can be exploited remotely, leading to resource exhaustion on the server.
What are the potential impacts of CVE-2025-26466?
The potential impacts of CVE-2025-26466 include service disruption due to excessive consumption of server resources.
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