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CVE-2011-3402

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Microsoft Windows. For every flaw being used in attacks, see Exploited flaws; for Microsoft’s, see Microsoft flaws being used in attacks.

CVE-2011-3402 is a security flaw in Microsoft Windows, Microsoft’s operating system for PCs and servers. Opening a booby-trapped file can let an attacker run their own code through Microsoft Windows. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 6 Oct 2025.[1]

Microsoft Windows is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Microsoft has published a fix or advice.

Description

CISA calls it a remote code execution in Microsoft Windows. In its words: “Microsoft Windows Kernel contains an unspecified vulnerability in the TrueType font parsing engine in win32k.sys in the kernel-mode drivers that allows remote attackers to execute arbitrary code via crafted font data in a Word document or web page.”[1]

The CVE record adds: “Unspecified vulnerability in the TrueType font parsing engine in win32k.sys in the kernel-mode drivers in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP2, Windows Server 2008 SP2, R2, and R2 SP1, and Windows 7 Gold and SP1 allows remote attackers to execute arbitrary code via crafted font data in a Word document or web page, as exploited in the wild in November 2011 by Duqu, aka "TrueType Font Parsing Vulnerability."”[2]

It scores 8.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record doesn’t list version ranges for it; Microsoft’s advisory has them[3]. CISA names the product as Microsoft Windows.

Every device with Microsoft Windows needs the update.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 6 Oct 2025, 5,085 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 27 Oct 2025 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 78%. That’s in the top 1% of the flaws it scores.[4]

CISA assesses it as not automatable: each attack takes some work.

CISA doesn’t say who was attacked, or how.

Fix

Microsoft has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]

  1. Update Microsoft Windows now.On Windows: Settings, Windows Update, Check for updates, then restart. Office updates come the same way, or from any Office app: File, Account, Update Options. Then turn on automatic updates, so the next fix arrives on its own.
  2. If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 8.8.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 78%.[4]

See also

Other Microsoft Windows flaws

Similar flaws

  • CVE-2026-111357, Ivanti Connect Secure: missing authentication for critical function ·
  • CVE-2026-97229, GitLab Community Edition and Enterprise Edition: integer overflow or wraparound ·
  • CVE-2026-76418, Cisco Secure Firewall ASA Software and Cisco Secure FTD Software: unchecked return value to NULL pointer dereference ·
  • CVE-2026-48356, Adobe Commerce and Magento: unrestricted upload of file with dangerous type ·
  • CVE-2026-111497, Google Brotli: unchecked return value ·

Added the same day

  • CVE-2025-61882, Oracle E-Business Suite: unspecified ·
  • CVE-2021-43226, Microsoft Windows: privilege escalation ·
  • CVE-2021-22555, Linux Kernel: heap out-of-bounds write ·
  • CVE-2013-3918, Microsoft Windows: out-of-bounds write ·
  • CVE-2010-3962, Microsoft Internet Explorer: uninitialized memory corruption ·

Every Microsoft flaw on CISA’s list · Everything added in October 2025

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Microsoft Windows Remote Code Execution Vulnerability”. Known Exploited Vulnerabilities Catalog, added 6 Oct 2025.
  2. ^ National Institute of Standards and Technology. “CVE-2011-3402 Detail”. National Vulnerability Database, published 4 Nov 2011.
  3. ^ Microsoft. Advisories and fixes: docs.microsoft.com, docs.microsoft.com, docs.microsoft.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.781, percentile 99.6, 31 Oct 2026.
  5. CVE Program. “CVE-2011-3402”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.