Always-Incorrect Control Flow Implementation in libssh - CVE-2026-59849
Published: July 27, 2026
Vulnerability identifier: #VU139532
CSH Severity: Low
CVSS v4: 2.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-59849
CWE-ID: CWE-670
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to improper state management in ssh_userauth_publickey_auto() when handling automatic public key authentication with configured certificates. A remote user can reject a configured certificate or trigger error handling for a missing configured certificate to cause a denial of service.
Only the client side is affected, and exploitation requires a specific configuration in which certificate-based automatic authentication is used; the infinite loop occurs when the server does not enforce an authentication limit.
Affected software
libssh
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for ARM 64
Ubuntu
libssh (Ubuntu package)
libssh (Red Hat package)
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for ARM 64
Ubuntu
libssh (Ubuntu package)
libssh (Red Hat package)
How to mitigate CVE-2026-59849
Install security update from vendor's website.
libssh - addressed in versions 0.11.5, 0.12.1
libssh (Ubuntu package) - addressed in versions 0.9.6-2ubuntu0.22.04.8, 0.10.6-2ubuntu0.5, 0.11.3-1ubuntu2.1
libssh (Red Hat package) - update to 0.12.0-3.el10_2
libssh (Ubuntu package) - addressed in versions 0.9.6-2ubuntu0.22.04.8, 0.10.6-2ubuntu0.5, 0.11.3-1ubuntu2.1
libssh (Red Hat package) - update to 0.12.0-3.el10_2