Attack Chain

1. The attacker identifies a service or application utilizing a vulnerable version of libssh.
2. The attacker crafts a malicious input string designed to trigger inefficient regular expression processing within libssh.
3. The attacker sends the crafted input to the vulnerable service via a network connection (e.g., SSH).
4. The libssh library attempts to process the malicious input using its regular expression engine.
5. The inefficient regular expression causes excessive CPU consumption or memory allocation.
6. The vulnerable service becomes unresponsive due to resource exhaustion, leading to a denial-of-service condition.
7. Subsequent legitimate requests to the service are blocked or delayed, further exacerbating the impact.

Impact

Successful exploitation of CVE-2026-0967 can result in a denial-of-service condition, rendering affected services or applications unavailable. The impact scope depends on the role of the affected system. For example, a critical server becoming unavailable could disrupt business operations. While the number of potential victims is unknown, any system utilizing a vulnerable version of libssh is susceptible. The defense evasion aspect could allow attackers to bypass security controls during the DoS.

Recommendation

• Identify systems using libssh and determine the installed version.
• Apply available patches or updates for libssh to remediate CVE-2026-0967 as released by Microsoft.
• Deploy the Sigma rule “Detect Suspicious Libssh Regex Processing” to monitor for potential exploitation attempts.
• Monitor CPU and memory usage on systems running libssh for unusual spikes, which may indicate a DoS attack.
• Implement rate limiting on services using libssh to mitigate the impact of DoS attacks.