CVE-2026-55199

Published Jun 17, 2026

Last updated 2 days ago

CVSS high 8.2
Port (22)

Overview

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.
Source
disclosure@vulncheck.com
NVD status
Awaiting Analysis

Risk scores

CVSS 4.0

Type
Secondary
Base score
8.2
Impact score
-
Exploitability score
-
Vector string
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Severity
HIGH

CVSS 3.1

Type
Secondary
Base score
5.9
Impact score
3.6
Exploitability score
2.2
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Severity
MEDIUM

Weaknesses

disclosure@vulncheck.com
CWE-835

Social media

Hype score
Not currently trending

  1. libssh2 Client-Side Heap-Overflow RCE (CVE-2026-55200) and Pre-Auth DoS (CVE-2026-55199) Direct: https://t.co/bvz86RVZmo https://t.co/0ipkD4wS4E

    @NewMaxxSSD

    24 Jun 2026

    30 Impressions

    0 Retweets

    0 Likes

    0 Bookmarks

    0 Replies

    0 Quotes

Related CVEs

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References

Sources include official advisories and independent security research.