Microsoft Forefront TMG Remote Code Execution Vulnerability (CVE-2011-1889)
Published In CISA KEV since Sources: CVE.org
What is affected, what to do
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."
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.
- Affected
- Microsoft Forefront Threat Management Gateway
eq 2010..2010
- Microsoft Forefront Threat Management Gateway
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Metrics
9.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
9.8
CVSS v3
Severity Critical on the scale from 0 to 10.
Source: CVE.org
49.0 %
EPSS score
Elevated — model estimates 10-50% exploitation likelihood.
Source: FIRST EPSS, percentile 98.9
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- 227.22 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- 9.8 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- 9.8
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- 49.0 %
- Elevated — model estimates 10-50% exploitation likelihood.
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- 98.9
- 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 · automatable · Technical impact: total
- Source: CISA Vulnrichment, as of 10 February 2025
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-119
Response and mitigation
Why act now?
Prioritisation rationale
This vulnerability is network-reachable without authentication or user interaction and gives full code execution. Despite its age, it remains among the CVEs with a very high likelihood of exploitation, although CISA does not flag known ransomware use. Typical targets are organisations with long-lived Microsoft estates, such as critical-infrastructure operators, public sector bodies and manufacturers, where TMG or its client survives as technical debt. If you can show the client is gone from your estate, the residual risk is low. Treat any installation you find as critical, especially on mobile endpoints, and remove or update it within the KEV deadline.
Runbook step 1
Immediate response (0-24 h)
- Inventory the affected component: The flaw is in the Forefront TMG Firewall Client Winsock provider installed on endpoints, not primarily in the TMG server. Use EDR, SCCM/Intune or your software inventory to locate every host running "Microsoft Forefront TMG Client" or the legacy "ISA Firewall Client". Example KQL (Defender):
DeviceTvmSoftwareInventory | where SoftwareName has_any ("forefront_tmg_client","firewall_client"). - Deploy the vendor fix: Microsoft shipped the TMG Firewall Client update under security bulletin MS11-040. Look up the exact KB number and fixed client build in the vendor advisory. Push it with priority to any client that cannot be uninstalled right away.
- Uninstall where possible: Forefront TMG 2010 is past end of support and no longer receives security updates. If the Firewall Client isn't strictly required (e.g. for authenticated non-HTTP proxying), remove it now. This is the most effective control.
- Contain exposed clients: Laptops running the client on untrusted networks (guest Wi-Fi, hotels, home offices without VPN) carry the highest risk. Disable the client on them or enforce always-on VPN until they are updated.
- Track exceptions: Record every asset that keeps the client as a legacy system with a formal, management-signed risk acceptance. You will need this as evidence for NIS2 and ISO 27001 A.8.8.
- Inventory the affected component: The flaw is in the Forefront TMG Firewall Client Winsock provider installed on endpoints, not primarily in the TMG server. Use EDR, SCCM/Intune or your software inventory to locate every host running "Microsoft Forefront TMG Client" or the legacy "ISA Firewall Client". Example KQL (Defender):
Runbook step 2
Mitigation layers
- Network segmentation: The Firewall Client control channel uses TCP/UDP 1745. Allow it only between client VLANs and your sanctioned TMG servers, and block 1745 at every other boundary, especially to and from the internet. This prevents a rogue host from posing as the TMG server.
- Configuration hardening: Pin the TMG server in the client configuration via GPO and disable auto-detection (WPAD/Auto-Detect). Otherwise, spoofed DHCP, DNS or WPAD responses can redirect clients to a malicious server.
- Anti-spoofing controls: Disable LLMNR and NetBIOS-NS via GPO, enable DHCP snooping and Dynamic ARP Inspection on access switches, and add a static
wpadblocklist entry in DNS. - Endpoint hardening: Enforce Exploit Protection system-wide (DEP, ASLR, CFG). Turn on ASR rules that block child processes from Office and browser processes. Remove local admin rights from users, because the code runs in the security context of the affected client application.
- Migration: Commit to a deadline for replacing TMG with a supported proxy or NGFW. Compensating controls on an unsupported product do not count as remediation.
Runbook step 3
Detection rules
- Crash telemetry: Watch the Windows Application log for Event ID 1000/1001 (Application Error / WER) where the faulting module belongs to the Firewall Client, e.g.
fwcwsp.dll. Clusters of these crashes in network-facing processes suggest exploitation attempts. SPL:index=wineventlog EventCode=1000 Faulting_Module_Name="fwc*". - Process ancestry (Sysmon EID 1 / EDR): Look for unexpected children (
cmd.exe,powershell.exe,rundll32.exe,mshta.exe) spawned by apps that use Winsock name resolution, such as browsers, mail clients and line-of-business apps. Sigma shape:ParentImage|endswith: [browser/app] AND Image|endswith: [LOLBins]. - Network telemetry (Zeek/Suricata): Flag TCP/UDP 1745 sessions to any destination not on your TMG server allowlist. Zeek:
conn.log id.resp_p == 1745 && id.resp_h !in tmg_servers. Configure a Suricata rule to alert on 1745 to unknown hosts. - Spoofing indicators: Anomalous WPAD queries and responses, plus rogue DHCP servers (DHCP snooping violations), in segments that contain Firewall Client hosts.
- Winsock catalog integrity: Sysmon EID 13 events showing registry changes under
HKLM\SYSTEM\CurrentControlSet\Services\WinSock2\Parameters\NameSpace_Catalog5outside maintenance windows.
- Crash telemetry: Watch the Windows Application log for Event ID 1000/1001 (Application Error / WER) where the faulting module belongs to the Firewall Client, e.g.
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
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."
Source: NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| microsoft | forefront_threat_management_gateway |
|
|
Vendors and products
Weakness classes (CWE)
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
Class
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
Entry at MITRE CWE-119
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
- securitytracker.com1025637Vulnerability database, x_refsource_SECTRACK, Broken link, Third-party advisory, Vulnerability database
- docs.microsoft.comMS11-040Vendor advisory, x_refsource_MS, Patch, Vendor advisory
- exchange.xforce.ibmcloud.comms-tmg-firewall-bo(67736)Vulnerability database, x_refsource_XF, Third-party advisory, Vulnerability database
- securityfocus.com48181Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
- secunia.com44857Third-party advisory, x_refsource_SECUNIA, Broken link
- oval.cisecurity.orgoval:org.mitre.oval:def:12642Vulnerability database, signature, x_refsource_OVAL, Broken link
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2011-1889government-resource, US government resource
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<a href="https://intel.neosec.eu/en/cve/CVE-2011-1889"><img src="https://intel.neosec.eu/badge/cve/CVE-2011-1889.svg?lang=en" alt="CVE-2011-1889 – NEOSEC Intel" height="20"></a>