CVE-2026-27917: Windows WFP NDIS Lightweight Filter Driver Use-After-Free Vulnerability

CVE-2026-27917 is a use-after-free vulnerability affecting the Windows WFP NDIS Lightweight Filter Driver (wfplwfs.sys). This vulnerability allows an attacker with local access and authorization to elevate their privileges on the system. The vulnerability arises from improper memory management within the driver, leading to a situation where a freed memory region is accessed again. The specific timeframe of exploitation in the wild is unknown, but the vulnerability was publicly disclosed on April 14, 2026. Successful exploitation could lead to complete system compromise for the attacker. Defenders should prioritize patching systems to mitigate this vulnerability.

Attack Chain

1. Attacker gains initial local access to the target system, potentially through social engineering or by exploiting another vulnerability.
2. The attacker leverages their existing privileges to interact with the Windows Filtering Platform (WFP).
3. The attacker crafts a specific request or operation that triggers the use-after-free condition within the wfplwfs.sys driver.
4. The driver attempts to access the freed memory region, leading to memory corruption.
5. The attacker manipulates the memory to overwrite critical system data structures.
6. The attacker triggers a system call or operation that utilizes the corrupted data.
7. Due to the overwritten data, the system grants elevated privileges to the attacker.
8. The attacker now has elevated privileges and can perform actions such as installing software, modifying data, and creating new accounts.

Impact

Successful exploitation of CVE-2026-27917 allows a local attacker to gain elevated privileges on a Windows system. This can lead to a complete compromise of the system, including data theft, malware installation, and further propagation of attacks within the network. While the number of victims and affected sectors is unknown, the high severity of the vulnerability warrants immediate attention from system administrators and security teams. A successful exploit grants the attacker full control over the compromised system.

Recommendation

• Apply the patch provided by Microsoft for CVE-2026-27917 as soon as possible to mitigate the use-after-free vulnerability in wfplwfs.sys (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-27917).
• Monitor for suspicious process creation events associated with wfplwfs.sys using process creation logs to detect potential exploitation attempts. Deploy the provided Sigma rules to your SIEM and tune them for your environment.
• Implement least privilege principles to limit the impact of a successful exploit by restricting user access rights.