🛡️ CVE-2026-55199 on Ubuntu — libssh2

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

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.

Distribution advisory

This page covers CVE-2026-55199 as tracked by Ubuntu, for the package libssh2. The fix is available in version 1.11.1-1ubuntu0.26.04.2; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity none, availability high.

Affected software

UBUNTU-CVE-2026-55199 is recorded against 1 package.

  • libssh2 (fixed in 1.11.1-1ubuntu0.26.04.2)

Timeline and source

Published on 17 June 2026 and last revised on 30 June 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

ubuntu.com (Report)
www.cve.org (Report)
github.com (Report)
ubuntu.com (Advisory)

Details

Severity Unknown
CVSS Score N/A
CVSS 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
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2026-06-17
Updated 2026-08-12
Modified 2026-06-30
Fix URL N/A

Affected Packages

Software From version Fixed in
libssh2 — 1.11.1-1ubuntu0.26.04.2

Similar Threats

Vulnerability Monitoring

Track new vulnerabilities in libssh2

UBUNTU-CVE-2026-55199 is rated CVSS 5.9 Medium. BotEraser monitors your WordPress installation and notifies you when software you use appears in our vulnerability database.

Set Up Free Alerts →

No credit card required  ·  Results in minutes

ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.