Quick answers
- Is CVE-2026-55200 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-55200 being exploited in the wild.
- How severe is CVE-2026-55200?
- High severity, with a CVSS score of 8.1, published 17 June 2026.
- Which products and versions are affected?
- Libssh2 through 1.11.1.
- Is there a fix for CVE-2026-55200?
- A patch was published on 2026-06-12: Fix merged into master branch via pull request 2052 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-55200 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-55200?
- Check whether you run Libssh2 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
An out-of-bounds (OOB) write vulnerability exists in the ssh2_transport_read() function within transport.c of libssh2. The root cause is a failure to enforce upper bounds on the packet_length field received from the network, leading to an integer overflow or buffer overflow (CWE-680) when processing excessively large values. A remote, unauthenticated attacker can exploit this by sending specially crafted SSH packets to corrupt heap memory. This memory corruption can result in a denial of service or remote code execution (RCE). The issue is fixed in commit 97acf3df (often referenced as 7acf3df) by adding boundary checks against LIBSSH2_PACKET_MAXPAYLOAD.
Affected products
- libssh2 libssh2 through 1.11.1
Timeline
- 2026-06-12: patched: Fix merged into master branch via pull request 2052
- 2026-06-17: disclosed: CVE published and advisory released by VulnCheck