---
id: CVE-2026-55200
title: >-
  libssh2 through 1.11.1, fixed in commit 7acf3df contains an out-of-bounds
  write vulnerability in ssh2_transport_read() that fails to enforce upper
  bounds on packet_length field
summary: >-
  libssh2 through 1.11.1, fixed in commit 7acf3df contains an out-of-bounds
  write vulnerability in ssh2_transport_read() that fails to enforce upper
  bounds on packet_length field. Remote attackers can send crafted SSH packets
  with excessiv…
severity: high
cvss: 8.1
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-680
vendor: libssh2
product: libssh2
affected:
  - libssh2 = 1.11.1
published: '2026-06-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:04:42.983'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55200'
references:
  - url: >-
      https://github.com/libssh2/libssh2/commit/97acf3dfda80c91c3a8c9f2372546301d4a1a7a8
    label: disclosure@vulncheck.com
  - url: 'https://github.com/libssh2/libssh2/pull/2052'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/libssh2-out-of-bounds-write-via-unchecked-packet-length-in-transport-c
    label: disclosure@vulncheck.com
  - url: >-
      https://web.archive.org/web/20260623211210/https://github.com/bikini/exploitarium/tree/main/libssh2-cve-2026-55200-poc
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - exploit-available
epss: 0.00825
epssPercentile: 0.55531
exploits:
  github: 3
  githubRepos:
    - 'https://github.com/0xBlackash/CVE-2026-55200'
    - 'https://github.com/xd20111/CVE-2026-55200'
    - 'https://github.com/kaleth4/CVE-2026-55200'
  checkedAt: '2026-09-25T08:21:03.154Z'
exploitAvailable: true
ingestedAt: '2026-09-17T17:23:30.592Z'
---

## Overview

libssh2 through 1.11.1, fixed in commit 7acf3df contains an out-of-bounds write vulnerability in ssh2_transport_read() that fails to enforce upper bounds on packet_length field. Remote attackers can send crafted SSH packets with excessively large packet_length values to corrupt heap memory and achieve remote code execution.

## Affected

- `libssh2 = 1.11.1`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.