CVE-2026-55199

Publication date 17 June 2026

Last updated 30 June 2026

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

5.9 · Medium

Score breakdown

Description

libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.

Status

Package Ubuntu Release Status
libssh2 26.04 LTS resolute
Fixed 1.11.1-1ubuntu0.26.04.2
25.10 questing
Fixed 1.11.1-1ubuntu0.25.10.2
24.04 LTS noble
Fixed 1.11.0-4.1ubuntu0.24.04.2
22.04 LTS jammy
Needs evaluation
20.04 LTS focal
Needs evaluation
18.04 LTS bionic
Needs evaluation
14.04 LTS trusty
Needs evaluation

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package Patch details
libssh2

Severity score breakdown

CVSS version:

Base score 8.2 · High

Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Base score 5.9 · Medium

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References

Related Ubuntu Security Notices (USN)

Other references

Access our resources on patching vulnerabilities