Vulnerability · Published Jun 17, 2026 · Assigned by VulnCheck
CVE-2026-55200libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c
High 8.1
In plain English
A high-severity security flaw in libssh2 from libssh2. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 3.9% (higher than 90% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.
Official description
libssh2 1.11.1, fixed in commit 97acf3d, 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.24 | chromium-rust | 1.96.1-r0 | ALPINE-CVE-2026-55200 |
| Alpine:v3.21 | libssh2 | 1.11.1-r2 | ALPINE-CVE-2026-55200 |
| Alpine:v3.22 | libssh2 | 1.11.1-r2 | ALPINE-CVE-2026-55200 |
| Alpine:v3.23 | libssh2 | 1.11.1-r3 | ALPINE-CVE-2026-55200 |
| Alpine:v3.24 | libssh2 | 1.11.1-r3 | ALPINE-CVE-2026-55200 |
| Alpine:v3.24 | rust | 1.96.1-r0 | ALPINE-CVE-2026-55200 |
| Debian:13 | libssh2 | 1.11.1-1+deb13u1 | DEBIAN-CVE-2026-55200 |
| Debian:14 | libssh2 | 1.11.1-4 | DEBIAN-CVE-2026-55200 |
| Ubuntu:25.10 | libssh2 | 1.11.1-1ubuntu0.25.10.2 | UBUNTU-CVE-2026-55200 |
| Ubuntu:26.04:LTS | libssh2 | 1.11.1-1ubuntu0.26.04.2 | UBUNTU-CVE-2026-55200 |
Affected products (as reported)
Weakness: CWE-680 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H