libssh2 Integer Overflow Vulnerability (CVE-2026-7598)

A remote integer overflow vulnerability has been identified in libssh2, a library implementing the SSH2 protocol. The vulnerability affects versions up to and including 1.11.1. The root cause lies in the userauth_password function within the src/userauth.c file. By manipulating the username_len and password_len arguments, an attacker can trigger an integer overflow. Successful exploitation could lead to denial of service or potentially remote code execution. The patch to address this vulnerability is identified as 256d04b60d80bf1190e96b0ad1e91b2174d744b1. Defenders should apply this patch to mitigate the risk.

Attack Chain

1. Attacker identifies a vulnerable libssh2 server or application.
2. Attacker initiates an SSH connection to the target.
3. The client begins the SSH authentication process.
4. The attacker crafts a malicious SSH password authentication request.
5. The request includes specially crafted username_len and password_len values designed to cause an integer overflow in the userauth_password function.
6. The userauth_password function processes the malicious lengths, resulting in an integer overflow.
7. The overflow leads to memory corruption or other unexpected behavior.
8. The corrupted memory can be exploited to cause a denial-of-service condition, or potentially, remote code execution.

Impact

Successful exploitation of this vulnerability could lead to a denial-of-service condition, disrupting services relying on the affected libssh2 library. In more severe scenarios, remote code execution might be possible, granting the attacker control over the affected system. While specific victim counts are unavailable, any system using a vulnerable version of libssh2 is potentially at risk.

Recommendation

• Apply the patch identified as 256d04b60d80bf1190e96b0ad1e91b2174d744b1 to remediate the integer overflow vulnerability.
• Deploy the Sigma rule “Detect libssh2 Integer Overflow Attempt” to identify potential exploitation attempts (see below).
• Monitor network traffic for unusually large username or password lengths during SSH authentication to detect suspicious activity.
• Upgrade to a version of libssh2 later than 1.11.1.