Infinite loop in libssh2 - CVE-2026-55199

Vulnerability identifier: #VU136048

CSH Severity: Medium

CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-55199

CWE-ID: CWE-835

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to infinite loop within the SSH_MSG_EXT_INFO handler in src/packet.c. A remote attacker can consume all available system resources and cause denial of service conditions.

libssh2
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 15 SP5
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 Server for SAP Applications 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Micro for Rancher
SUSE Linux Enterprise Micro
SUSE Linux Micro
Fedora
Basesystem Module
openSUSE Leap
openEuler
Anolis OS
Ubuntu
libssh2
libssh2-debuginfo
libssh2-debugsource
libssh2-help
libssh2-devel
libssh2_org-debugsource
libssh2-1-debuginfo
libssh2-1
libssh2 (Ubuntu package)
libssh2-docs
libssh2-1-32bit
libssh2-1-32bit-debuginfo
libssh2-1-64bit
libssh2-1-64bit-debuginfo

Install updates from vendor's repository.

libssh2 - addressed in versions 1.10.0-10, 1.11.0-7, 1.11.0-8
libssh2-debuginfo - addressed in versions 1.10.0-10, 1.11.0-7, 1.11.0-8
libssh2-debugsource - addressed in versions 1.10.0-10, 1.11.0-7, 1.11.0-8
libssh2-help - addressed in versions 1.10.0-10, 1.11.0-7, 1.11.0-8
libssh2-devel - addressed in versions 1.10.0-10, 1.11.0-7, 1.11.0-8
libssh2_org-debugsource - addressed in versions 1.11.0-3.1, 1.11.0-150000.4.32.1, 1.11.0-150200.9.5.1, 1.11.0-150600.20.3.1
libssh2-1-debuginfo - addressed in versions 1.11.0-3.1, 1.11.0-150000.4.32.1, 1.11.0-150200.9.5.1, 1.11.0-150600.20.3.1
libssh2-1 - addressed in versions 1.11.0-3.1, 1.11.0-150000.4.32.1, 1.11.0-150200.9.5.1, 1.11.0-150600.20.3.1
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 - update to 1.11.0-6
libssh2-devel - update to 1.11.0-6
libssh2-docs - update to 1.11.0-6
libssh2-1-32bit - addressed in versions 1.11.0-150000.4.32.1, 1.11.0-150200.9.5.1, 1.11.0-150600.20.3.1
libssh2-devel - addressed in versions 1.11.0-150200.9.5.1, 1.11.0-150600.20.3.1
libssh2-1-32bit-debuginfo - update to 1.11.0-150600.20.3.1
libssh2-1-64bit - update to 1.11.0-150600.20.3.1
libssh2-1-64bit-debuginfo - update to 1.11.0-150600.20.3.1
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

• https://www.openwall.com/lists/oss-security/2026/06/23/10
• https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4
• https://github.com/libssh2/libssh2/pull/1864

• Multiple vulnerabilities in libssh2
• Ubuntu update for libssh2
• Fedora 43 update for libssh2
• Fedora 44 update for libssh2
• Fedora EPEL 10.2 update for libssh2
• Fedora EPEL 10.3 update for libssh2
• Fedora EPEL 9 update for libssh2
• SUSE update for libssh2_org
• SUSE update for libssh2_org
• SUSE update for libssh2_org
• SUSE update for libssh2_org
• Anolis OS update for libssh2
• openEuler 24.03 LTS SP3 update for libssh2
• openEuler 24.03 LTS SP1 update for libssh2
• openEuler 22.03 LTS SP4 update for libssh2
• openEuler 24.03 LTS SP4 update for libssh2