CVE-2026-55199 | libssh2 through 1.11.1, fixed in commit 1762685, contains a … | CVSS 5.9 MEDIUM

Description

libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.

Metadata

CVE ID: CVE-2026-55199
State: PUBLISHED
Assigner: VulnCheck
Reserved: 2026-06-16 15:53 UTC
Published: 2026-06-17 18:44 UTC
Last updated: 2026-06-17 18:44 UTC
Primary CWE: CWE-835
Loop with Unreachable Exit Condition ('Infinite Loop')
Vendor / Product: libssh2 / libssh2
Sources: cve.org · NVD

Severity & Metrics

5.9 MEDIUM CVSS 3.1

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products (1)

Vendor	Product	Platform	Versions
libssh2	libssh2	—	0 ≤ 1.11.1, 17626857d20b3c9a1addfa45979dadcee1cd84a4

Weakness (CWE)

CWE	Source	Description
CWE-835	cna	Loop with Unreachable Exit Condition ('Infinite Loop')

CVSS scores (2)

Score	Severity	Version	Source	Vector
8.2	HIGH	4.0	cna	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
5.9	MEDIUM	3.1	cna	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References (3)