OESA-2026-3015

libssh2 is a library implementing the SSH2 protocol as defined by Internet Drafts: SECSH-TRANS(22), SECSH-USERAUTH(25), SECSH-CONNECTION(23), SECSH-ARCH(20), SECSH-FILEXFER(06)*, SECSH-DHGEX(04), and SECSH-NUMBERS(10).

Security Fix(es):

libssh2 through 1.11.1, fixed in commit 2dae302, contains an out-of-bounds heap read vulnerability in the sftpsymlink() function in src/sftp.c that allows a malicious SSH server or man-in-the-middle attacker to disclose heap memory contents or cause a crash by sending a crafted SSHFXPNAME response. Attackers can supply a linklen value larger than the actual packet data in SSHFXPNAME responses for SFTP READLINK and REALPATH operations, triggering a heap buffer over-read of up to target_len minus one bytes due to the missing validation of available packet buffer size before the memcpy operation.(CVE-2025-15661)

libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSHMSGEXTINFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nrextensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from libssh2get_string() are unchecked and the session timeout does not apply to CPU-bound loops.(CVE-2026-55199)