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
Fedora
Ubuntu
libssh2 (Ubuntu package)
libssh2
Fedora
Ubuntu
libssh2 (Ubuntu package)
libssh2
How to mitigate CVE-2026-55200
Install updates from vendor's repository.
libssh2 (Ubuntu package) - addressed in versions 1.11.0-4.1ubuntu0.24.04.2, 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
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