libssh2 1.11.1 OOB Write in ssh2_transport_read() via oversized packet_length
CVE-2026-55200 Published on June 17, 2026
libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c
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.
Vulnerability Analysis
CVE-2026-55200 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. Public availability of a proof of concept (POC) exploit exists for CVE-2026-55200. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
Integer Overflow to Buffer Overflow
The product performs a calculation to determine how much memory to allocate, but an integer overflow can occur that causes less memory to be allocated than expected, leading to a buffer overflow.
Products Associated with CVE-2026-55200
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Affected Versions
libssh2:- Before and including 1.11.1 is affected.
- Version 7acf3dfda80c91c3a8c9f2372546301d4a1a7a8 is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.