Infinite loop in libssh - CVE-2026-59843

Vulnerability identifier: #VU139526

CSH Severity: Low

CVSS v4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-59843

CWE-ID: CWE-835

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote user to cause a denial of service.

The vulnerability exists due to an infinite loop in channel_write_common() when processing an SSH_MSG_CHANNEL_OPEN request with a maximum packet length of zero. A remote user can send a specially crafted channel open request to cause a denial of service.

Repeating the attack over multiple connections can exhaust CPU resources of the server.

libssh
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Micro
SUSE Linux Enterprise Micro for Rancher
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for ARM 64
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power, little endian
Basesystem Module
openSUSE Leap
openEuler
Ubuntu
libssh-debugsource
libssh-debuginfo
libssh
libssh-help
libssh-devel
libssh (Ubuntu package)
libssh4-64bit
libssh4-64bit-debuginfo
libssh4-32bit
libssh4-32bit-debuginfo
libssh4
libssh4-debuginfo
libssh-config
libssh (Red Hat package)
Netezza Appliance - Cyclops

Install security update from vendor's website.

libssh - addressed in versions 0.11.5, 0.12.1
libssh-debugsource - addressed in versions 0.9.4-21, 0.9.6-21, 0.10.5-15
libssh-debuginfo - addressed in versions 0.9.4-21, 0.9.6-21, 0.10.5-15
libssh - addressed in versions 0.9.4-21, 0.9.6-21, 0.10.5-15
libssh-help - addressed in versions 0.9.4-21, 0.9.6-21, 0.10.5-15
libssh-devel - addressed in versions 0.9.4-21, 0.9.6-21, 0.10.5-15
libssh (Ubuntu package) - addressed in versions 0.9.6-2ubuntu0.22.04.8, 0.10.6-2ubuntu0.5, 0.11.3-1ubuntu2.1
libssh-debugsource - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh4-64bit - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh4-64bit-debuginfo - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh4-32bit - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh4-32bit-debuginfo - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh4 - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh4-debuginfo - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh-config - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh-devel - addressed in versions 0.9.8-150400.3.20.1, 0.9.8-150600.11.15.1
libssh (Red Hat package) - addressed in versions 0.10.4-19.el9_8, 0.12.0-3.el10_2
Netezza Appliance - Cyclops - update to 11.3.1.4

• https://www.libssh.org/security/advisories/CVE-2026-59843.txt
• https://git.libssh.org/projects/libssh.git/commit/?id=44b186fa17aff497dae420c59c003222e438103c

• Multiple vulnerabilities in libssh
• SUSE update for libssh
• SUSE update for libssh
• openEuler 24.03 LTS SP3 update for libssh
• openEuler 24.03 LTS SP1 update for libssh
• openEuler 22.03 LTS SP4 update for libssh
• openEuler 20.03 LTS SP4 update for libssh
• Red Hat Enterprise Linux 10 update for libssh
• openEuler 24.03 LTS SP4 update for libssh
• Ubuntu update for libssh
• Red Hat Enterprise Linux 9 update for libssh
• Multiple vulnerabilities in IBM Netezza Appliance - Cyclops