Microsoft Ancillary Function Driver (afd.sys) Improper Input Validation Vulnerability (CVE-2011-2005)
Published In CISA KEV since Sources: CVE.org
What is affected, what to do
afd.sys in the Ancillary Function Driver in Microsoft Windows XP SP2 and SP3 and Server 2003 SP2 does not properly validate user-mode input passed to kernel mode, which allows local users to gain privileges via a crafted application, aka "Ancillary Function Driver Elevation of Privilege 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
7.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
7.8
CVSS v3
Severity High on the scale from 0 to 10.
Source: CVE.org
31.8 %
EPSS score
Elevated — model estimates 10-50% exploitation likelihood.
Source: FIRST EPSS, percentile 98.3
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- 216.30 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- 7.8 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- 7.8
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- 31.8 %
- 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- 98.3
- 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 10 February 2025
Response and mitigation
Why act now?
Prioritisation rationale
This CVE is on KEV because a mature, publicly available exploit gives reliable local privilege escalation to SYSTEM. Attackers chain it as a second stage after initial access (phishing, stolen credentials, web shells), and exploitation likelihood is rated very high. CISA does not flag known ransomware use. Typical victims are forgotten XP and 2003 systems in manufacturing, medical devices, building automation and line-of-business applications at critical-infrastructure operators. Because these unsupported boxes are rarely monitored, they often become a persistent foothold in the network. If your estate has no such systems, residual risk is negligible. Treat any network-connected XP/2003 host you find as high priority, with isolation and replacement as the primary fixes.
Runbook step 1
Immediate response (0-24 h)
- Inventory every Windows XP SP2/SP3 and Windows Server 2003 SP2 host via CMDB, an AD query (
Get-ADComputer -Filter {OperatingSystem -like "*XP*" -or OperatingSystem -like "*2003*"}) and network scanning (SMB OS fingerprinting). Both platforms have been out of vendor support for years, so treat every hit as a high-risk asset. - Apply the patch if it is still missing: the afd.sys security update is available from the vendor. Look up the bulletin and KB number in the vendor advisory. Verify the patch level by comparing the file version of
%SystemRoot%\System32\drivers\afd.sysagainst the advisory. - Isolate legacy hosts that cannot be migrated immediately, such as OT HMIs, lab instruments or POS terminals. Move them into a dedicated default-deny VLAN and allow only explicitly required flows.
- Restrict interactive and remote logons: exploitation requires local code execution. Disable RDP (TCP 3389) from user networks and remove unneeded local and domain accounts. Allow only named admins via a jump-host chain.
- Rotate privileged credentials used on or cached by affected hosts (local admin, service accounts, domain admins). After an escalation to SYSTEM, assume LSA secrets and hashes are compromised.
- Escalate the migration decision: record replacement or decommissioning in the risk register (ISO 27001 A.8.8 / NIS2 Art. 21) with a named owner and deadline.
- Inventory every Windows XP SP2/SP3 and Windows Server 2003 SP2 host via CMDB, an AD query (
Runbook step 2
Mitigation layers
- Network segmentation: block legacy hosts from reaching the internet and Tier-0 assets (DCs, PKI, backup). Allow inbound SMB (TCP 445/139) and RPC (TCP 135) only from management hosts.
- Application control: enforce Software Restriction Policies (SRP, available on XP/2003) in allow-list mode. Block execution from
%TEMP%,%APPDATA%,%USERPROFILE%\Downloadsand removable media. Without a runnable exploit binary, local exploitation becomes much harder. - IAM / least privilege: standard users get no admin rights. Disable the Guest account and anonymous access (
RestrictAnonymous=2). Eliminate shared accounts on legacy systems. - Endpoint hardening: run a still-supported AV/EDR where the vendor covers XP/2003. Public exploit modules and compiled PoCs for this flaw are well signatured. Disable AutoRun/AutoPlay and restrict USB mass storage.
- IPS/NDR: enable Suricata/Snort rule sets for post-exploitation activity such as Meterpreter staging, reverse shells and SMB lateral movement at the boundaries of the legacy VLANs.
Runbook step 3
Detection rules
- SYSTEM-context process spawned from a user process: on XP/2003 the Security log emits Event ID 592 (process created) rather than 4688. Alert when
cmd.exeorpowershell.exeruns asNT AUTHORITY\SYSTEMunder a parent that was running as a standard user. Sigma shape:EventID=592 AND SubjectUser="SYSTEM" AND ParentImage NOT IN (services.exe, winlogon.exe, svchost.exe). - Execution from user-writable paths: watch Event 592 or EDR process telemetry for
Imageunder\Temp\,\Application Data\or\Documents and Settings\*\Desktop\, followed within seconds by a SYSTEM child process. - Service installs and account changes after escalation: on XP/2003 these are Security events 601 (service install) and 624/636 (account created or added to local Administrators), plus System log 7035/7036. SPL:
index=wineventlog host IN (legacy_hosts) EventCode IN (601,624,636). - Network telemetry (Zeek/Suricata): look for new outbound connections from legacy VLANs to unknown destinations, e.g. reverse shells on TCP 4444 or 443 without TLS SNI. Also flag admin-share access (
ADMIN$,C$) from legacy hosts to other machines (Zeeksmb_files.log,smb_mapping.log). - Driver file integrity: use FIM to track the version and hash of
afd.sys. Flag any regression to an unpatched build, for example after an image restore.
- SYSTEM-context process spawned from a user process: on XP/2003 the Security log emits Event ID 592 (process created) rather than 4688. Alert when
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
afd.sys in the Ancillary Function Driver in Microsoft Windows XP SP2 and SP3 and Server 2003 SP2 does not properly validate user-mode input passed to kernel mode, which allows local users to gain privileges via a crafted application, aka "Ancillary Function Driver Elevation of Privilege Vulnerability."
Source: NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)
Vendors and products
Affected operating systems
| Windows | microsoft | windows_server_2003 | — |
| 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
- oval.cisecurity.orgoval:org.mitre.oval:def:13114Vulnerability database, signature, x_refsource_OVAL, Broken link
- docs.microsoft.comMS11-080Vendor advisory, x_refsource_MS, Patch, Vendor advisory
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2011-2005government-resource, US government resource
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<a href="https://intel.neosec.eu/en/cve/CVE-2011-2005"><img src="https://intel.neosec.eu/badge/cve/CVE-2011-2005.svg?lang=en" alt="CVE-2011-2005 – NEOSEC Intel" height="20"></a>