Buffer Overflow Affecting libssh2 package, versions *


Severity

Recommended
high

Based on CentOS security rating.

Threat Intelligence

EPSS
0.32% (25th percentile)

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  • Snyk IDSNYK-CENTOS7-LIBSSH2-18324275
  • published27 Jul 2026
  • disclosed24 Jul 2026

Introduced: 24 Jul 2026

NewCVE-2026-66035  (opens in a new tab)
CWE-120  (opens in a new tab)

How to fix?

There is no fixed version for Centos:7 libssh2.

NVD Description

Note: Versions mentioned in the description apply only to the upstream libssh2 package and not the libssh2 package as distributed by Centos. See How to fix? for Centos:7 relevant fixed versions and status.

libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.

CVSS Base Scores

version 3.1