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Actively exploited

CVE-2011-1889 Microsoft Forefront TMG Remote Code Execution Vulnerability

A remote code execution vulnerability exists in the Forefront Threat Management Gateway (TMG) Firewall Client Winsock provider that could allow code execution in the security context of the client application.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 3 Mar 2022.
  • Rated Critical severity (CVSS 9.8, scored by CISA).
  • This product type is often exposed to the internet, which is where attackers scan for it first.
  • It has been in the catalogue for 1,709 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

The NSPLookupServiceNext function in the client in Microsoft Forefront Threat Management Gateway (TMG) 2010 allows remote attackers to execute arbitrary code via vectors involving unspecified requests, aka "TMG Firewall Client Memory Corruption Vulnerability."

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Microsoft Forefront Threat Management Gateway (TMG). Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply updates per vendor instructions.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 24 Mar 2022 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2011-1889
  3. CVE record: CVE-2011-1889
  4. FIRST EPSS
  5. securitytracker.com/id?1025637
  6. docs.microsoft.com/en-us/security-updates/securitybulletins/2011/ms11-040
  7. exchange.xforce.ibmcloud.com/vulnerabilities/67736
  8. securityfocus.com/bid/48181
  9. secunia.com/advisories/44857
  10. oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A12642