Critical libssh2 Vulnerability CVE-2026-55200 Enables Remote Code Execution

### Executive summary A critical libssh2 vulnerability (CVE-2026-55200, CVSS 9.2) allows unauthenticated remote attackers to trigger an out-of-bounds write during SSH packet processing by abusing an unchecked packet_length in ssh2_transport_read(), potentially enabling remote code execution; the issue affects releases up to 1.11.1, a patch commit has been published, and no in-the-wild exploitation has been confirmed.