Out-of-bounds write in libssh2 - CVE-2026-55200

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Main Vulnerability Database Vulnerabilities #VU136046

Out-of-bounds write in libssh2 - CVE-2026-55200

Published: July 1, 2026 / Updated: August 6, 2026


Vulnerability identifier: #VU136046
CSH Severity: Critical
CVSS v4: 9.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-55200
CWE-ID: CWE-787
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote attacker to compromise vulnerable system.

The vulnerability exists due to a boundary error when processing untrusted input within the ssh2_transport_read() function. A remote attacker can send specially crafted SSH packets with overly long packet_length values, trigger an out-of-bounds write and execute arbitrary code on the target system.


Affected software

libssh2
Gentoo Linux
Debian Linux
Fedora
Ubuntu
PeopleSoft Enterprise PeopleTools
libssh2-1t64 (Ubuntu package)
libssh2
net-libs/libssh2
libssh2 (Debian package)

How to mitigate CVE-2026-55200

Install updates from vendor's repository.

libssh2-1t64 (Ubuntu package) - addressed in versions 1.11.1-1ubuntu0.25.10.2, 1.11.1-1ubuntu0.26.04.2
libssh2 - addressed in versions 1.11.1-8.el9, 1.11.1-8.el10_2, 1.11.1-8.el10_3, 1.11.1-8.fc43, 1.11.1-8.fc44
net-libs/libssh2 - update to 1.11.1-r2
libssh2 (Debian package) - update to 1.11.1-1+deb13u1

External References

Related Security Bulletins