CVE-2026-40413: Windows TCP/IP Null Pointer Dereference Denial of Service

CVE-2026-40413 is a security vulnerability affecting Windows TCP/IP. The vulnerability, a null pointer dereference, allows an unauthorized attacker within an adjacent network to trigger a denial-of-service (DoS) condition. This vulnerability was published on May 12, 2026, and has a CVSS v3.1 score of 7.4. Exploitation of this vulnerability could disrupt network services and impact the availability of affected Windows systems. Defenders should apply the patch released by Microsoft to mitigate the risk.

Attack Chain

1. The attacker gains access to a network adjacent to the target Windows system.
2. The attacker sends a specially crafted TCP/IP packet to the target system.
3. The Windows TCP/IP stack attempts to process the malicious packet.
4. During packet processing, a null pointer is dereferenced due to the crafted packet’s structure.
5. The null pointer dereference causes the TCP/IP service to crash.
6. The crashed TCP/IP service leads to a denial-of-service condition, preventing legitimate network communication.
7. The target system becomes unresponsive to network requests.

Impact

Successful exploitation of CVE-2026-40413 leads to a denial-of-service condition on the targeted Windows system. This can disrupt network services, impacting availability and potentially causing data loss or corruption if critical processes are interrupted. The vulnerability can be exploited by an attacker on an adjacent network, increasing the risk in environments with shared network infrastructure.

Recommendation

• Apply the security update provided by Microsoft to patch CVE-2026-40413 as referenced in the advisory URL.
• Monitor network traffic for anomalous TCP/IP packets originating from adjacent networks using the Sigma rule “Detect CVE-2026-40413 Exploitation Attempt — Suspicious TCP Packet”.
• Enable network intrusion detection systems to identify and block potentially malicious TCP/IP packets.