Microsoft Windows Remote Code Execution Vulnerability (CVE-2011-3402)
Published In CISA KEV since Sources: pwn.watch, CVE.org
What is affected, what to do
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."
The vulnerability is being actively exploited; treat it as a priority. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.
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Metrics
8.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
8.8
CVSS v3
Severity High on the scale from 0 to 10.
Source: pwn.watch, CVE.org
78.1 %
EPSS score
High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
Source: FIRST EPSS, percentile 99.58
Show all metrics
- Severity
- Critical
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 223.33 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- actively exploited
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 8.8 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 8.8
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 78.1 %
- High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 99.58
- Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- Actively exploited
- Published
In CISA KEV since
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- CISA assessment (SSVC)
- Exploitation: active · not automatable · Technical impact: total
- Source: CISA Vulnrichment, as of 4 October 2025
Response and mitigation
Why act now?
Prioritisation rationale
This is a kernel-level code-execution bug triggered by a crafted Word document or web page. It is network-reachable without authentication and needs only a user to open content. It was first seen in the Duqu espionage toolkit. Its KEV listing and its position among the CVEs most likely to be exploited reflect how easily it can still be weaponised against unpatched estates. CISA reports no known ransomware use. For organisations with a fully current client fleet, residual risk is low. In KRITIS and OT environments still running Windows XP/7 (HMIs, engineering workstations, medical devices), treat it as a high-priority finding — especially where those systems have email or web access.
Runbook step 1
Immediate response (0-24 h)
- Inventory: Identify every host running Windows XP, Server 2003, Vista, Server 2008 / 2008 R2 or Windows 7 (CMDB, EDR asset list,
Get-ADComputer -Filter * -Properties OperatingSystem). All of these platforms are end-of-life — treat them as high-risk assets. - Verify patch state: Microsoft fixed this in Security Bulletin MS11-087 (KB2639417, win32k.sys). A follow-up update for co-affected components (Office, .NET, Silverlight, Lync) shipped as MS12-034. Check with
wmic qfe | findstr 2639417or your patch tooling and deploy anything missing now. Look up the exact per-product KB mapping in the vendor advisory. - Isolate unpatched legacy hosts: Cut systems lacking MS11-087 off from internet browsing and email. Move them into a legacy segment. No external Office documents or web access on these machines.
- Apply the workaround where patching is impossible: Deny access to
t2embed.dll(the Microsoft workaround from Security Advisory 2639658):takeown /f %windir%\system32\t2embed.dllthenicacls %windir%\system32\t2embed.dll /deny *S-1-1-0:(F). Repeat for%windir%\SysWOW64\t2embed.dllon x64. Side effect: embedded fonts will no longer render. - Tighten the mail gateway: Quarantine external Office documents carrying embedded fonts (
.odttf, embedded TrueType objects) until patch coverage is confirmed.
- Inventory: Identify every host running Windows XP, Server 2003, Vista, Server 2008 / 2008 R2 or Windows 7 (CMDB, EDR asset list,
Runbook step 2
Mitigation layers
- Network segmentation: Place EOL Windows systems in a dedicated VLAN with allowlist-only egress (internal WSUS and line-of-business servers only). Block direct HTTP/HTTPS egress on ports 80/443.
- Proxy / IPS: Block webfont downloads (
.ttf,.eot,.otf,.woff) to legacy segments. Enable MS11-087 / Duqu TrueType signatures in your Suricata or Snort ruleset — grep the ET/Talos rules forcve,2011-3402. - Endpoint hardening: On modern estate (Windows 10 and later), enable the "Untrusted Font Blocking" GPO as defence-in-depth against future font-parsing bugs. Enforce Office Protected View and "Block macros from the Internet".
- Office configuration: Restrict legacy file formats via Trust Center File Block Settings. Open external documents only in Protected View or Application Guard.
- IAM / least privilege: Exploitation lands in kernel context, so standard-user rights won't contain it. Never log on with privileged accounts (Domain Admins) to EOL hosts — this limits credential theft after a compromise.
Runbook step 3
Detection rules
- Sysmon EID 1 / Windows Event 4688: Look for Office spawning suspicious children:
ParentImageending\WINWORD.EXEwithImageending\cmd.exe,\powershell.exe,\rundll32.exeor\regsvr32.exe. Sigma shape:selection: ParentImage|endswith: '\WINWORD.EXE' AND Image|endswith: ['\cmd.exe','\rundll32.exe']. - Crashes as failed-exploit signals: Watch for System log Event ID 1001 (BugCheck) or Event ID 41 (Kernel-Power) referencing
win32k.sys. KQL:Event | where EventID == 1001 and RenderedDescription has "win32k". Investigate clusters of BSODs shortly after a document or page was opened. - Sysmon EID 11 / EID 6: Flag new
.sysfiles written or unsigned drivers loaded right after Office activity — Duqu dropped kernel drivers. SPL:index=sysmon EventCode=6 Signed=false. - Network telemetry (Zeek
files.log/http.log): Flag font MIME types (application/x-font-ttf,application/vnd.ms-fontobject) delivered to EOL hosts. Also flag external DOCX attachments containing embeddedword/fonts/*.odttf. - EDR process ancestry: Alert on
outlook.exe → winword.exe → injection into svchost.exe/lsass.exe, or unusual outbound connections fromwinword.exeimmediately after a document opens.
- Sysmon EID 1 / Windows Event 4688: Look for Office spawning suspicious children:
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
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."
Source: pwn.watch, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)
Vendors and products
Affected operating systems
| Windows | microsoft | windows_7 | — |
| Windows | microsoft | windows_server_2003 | — |
| Windows | microsoft | windows_server_2008 | — |
| Windows | microsoft | windows_vista | — |
| Windows | microsoft | windows_xp | — |
Public exploit references
Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.
| CISA KEV Catalog | CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov | actively exploited |
References & sources
- secunia.com49121Third-party advisory, x_refsource_SECUNIA, Vendor advisory
- oval.cisecurity.orgoval:org.mitre.oval:def:15645Vulnerability database, signature, x_refsource_OVAL, Broken link
- us-cert.govTA12-164AThird-party advisory, x_refsource_CERT, US government resource
- blogs.mcafee.commcafee-labs/the-day-of-the-golden-jackal-–-further-tales-of-the…x_refsource_MISC, Broken link
- securitytracker.com1027039Vulnerability database, x_refsource_SECTRACK, Broken link
- secunia.com49122Third-party advisory, x_refsource_SECUNIA, Vendor advisory
- docs.microsoft.comMS11-087Vendor advisory, x_refsource_MS, Vendor advisory, pwn-watch
- symantec.comcontent/en/us/enterprise/media/security_response/whitepapers/w3…x_refsource_MISC, Not applicable
- us-cert.govTA11-347AThird-party advisory, x_refsource_CERT, US government resource
- oval.cisecurity.orgoval:org.mitre.oval:def:13998Vulnerability database, signature, x_refsource_OVAL, Broken link
- us-cert.govcontrol_systems/pdf/ICS-ALERT-11-291-01E.pdfx_refsource_MISC, US government resource
- securelist.comen/blog/208193197/The_Mystery_of_Duqu_Part_Twox_refsource_MISC, Not applicable
- technet.microsoft.comsecurity/advisory/2639658x_refsource_CONFIRM, Vendor advisory
- docs.microsoft.comMS12-034Vendor advisory, x_refsource_MS, Vendor advisory
- docs.microsoft.comMS12-039Vendor advisory, x_refsource_MS, Vendor advisory
- oval.cisecurity.orgoval:org.mitre.oval:def:15290Vulnerability database, signature, x_refsource_OVAL, Broken link
- isc.sans.edudiary/Duqu+Mitigation/11950x_refsource_MISC, Third-party advisory
- symantec.comconnect/w32-duqu_status-updates_installer-zero-day-exploitx_refsource_MISC, Not applicable
- us-cert.govTA12-129AThird-party advisory, x_refsource_CERT, US government resource
- blogs.technet.comb/msrc/archive/2011/11/03/microsoft-releases-security-advisory-…x_refsource_CONFIRM, Vendor advisory
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<a href="https://intel.neosec.eu/en/cve/CVE-2011-3402"><img src="https://intel.neosec.eu/badge/cve/CVE-2011-3402.svg?lang=en" alt="CVE-2011-3402 – NEOSEC Intel" height="20"></a>