Windows Kernel TrueType Font Parsing Vulnerability (CVE-2011-3402)

Historical catalog analysis: CISA added this entry on October 06, 2025. The entry reflects catalog information retrieved on August 31, 2026, not a snapshot archived on the inclusion date. Check current vendor guidance before acting.

What the vulnerability is

CVE-2011-3402 is a remote code execution (RCE) vulnerability located within the Microsoft Windows kernel. Specifically, the flaw exists in the TrueType font parsing engine housed in the win32k.sys kernel-mode driver. This vulnerability allows an attacker to execute arbitrary code with kernel-level privileges if a user processes specially crafted font data.

Exposure and applicability

The exposure path is primarily delivery-based. An attacker can trigger the vulnerability by inducing a system to parse malicious font data, which may be embedded in a Word document or hosted on a web page. Because the flaw resides in win32k.sys, successful exploitation occurs within the kernel mode, significantly increasing the potential impact compared to user-mode execution.

Remediation priorities

Our analysis suggests that remediation should prioritize systems that frequently process external documents or render untrusted web content. Based on the source data, the following actions are prioritized:

1. Patch Deployment: Apply the updates specified in vendor security bulletin MS11-087. This is the primary method for addressing the underlying flaw in the font parsing engine.
2. Cloud Service Alignment: For organizations utilizing cloud services, we recommend aligning remediation timelines with BOD 22-01 guidance where applicable to ensure consistent exposure reduction across hybrid environments.
3. Product Decommissioning: In scenarios where mitigations cannot be applied or verified, our analysis suggests discontinuing the use of the affected product version to eliminate the attack surface entirely.

How to validate remediation

Verification must go beyond confirming a patch installation date or checking a version number, as these do not prove the kernel state is secure. To verify that exposure has been reduced, defenders should:

• Verify Driver Integrity: Confirm that the win32k.sys binary on the host matches the version and hash provided in the vendor’s updated security release.
• Configuration Audit: Ensure that no legacy or unpatched versions of the font parsing engine remain active in the environment through a comprehensive inventory of kernel-mode drivers.

Limits and open questions

While patching addresses the known flaw, residual risk remains if other undiscovered vulnerabilities exist within the same parsing engine. The source does not provide information on whether this vulnerability is currently being leveraged by ransomware campaigns, leaving the current active threat level unknown. Furthermore, the effectiveness of third-party security software in detecting the delivery of crafted font data prior to kernel processing is not established.

Source and editorial note

CVE-2011-3402: Microsoft Windows Remote Code Execution Vulnerability · Source date: October 06, 2025 · Retrieved August 31, 2026.

Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.

Archive date: October 09, 2025. The displayed post date is assigned three days after the source date to organize this retrospective archive; it does not mean this site published the analysis then. First published by this site: October 01, 2026 at 00:15 UTC.

Request a Vulnerability Assessment