---
id: "CVE-2011-2005"
kind: "vulnerability"
aliases: ["CVE-2011-2005"]
title: "Microsoft Ancillary Function Driver (afd.sys): Microsoft Ancillary Function Driver (afd.sys) Improper Input Validation Vulnerability"
severity: "high"
cvss: 7.8
epss: 0.31761
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Microsoft Ancillary Function Driver (afd.sys)", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "infrastructure", "multi-user-hosts", "terminal-servers", "windows"]
not_affected_if: ["non-windows", "patched-windows"]
published_at: "2011-10-12T02:52:43+00:00"
first_seen_at: "2026-10-23T19:11:52+00:00"
updated_at: "2026-10-23T21:57:35+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2011-2005", "first_seen_at": "2026-10-23T19:11:52+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2011-2005", "first_seen_at": "2026-10-23T19:13:45+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2011-2005", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Microsoft Ancillary Function Driver (afd.sys): Microsoft Ancillary Function Driver (afd.sys) Improper Input Validation Vulnerability

Microsoft Windows afd.sys, the kernel driver behind Winsock socket calls, does not validate user-mode input passed to kernel mode. A local user running a crafted application can escalate to kernel-level privileges.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Microsoft Ancillary Function Driver (afd.sys) affected ? fixed ?

## Fix

Apply the Microsoft updates for this CVE per vendor instructions, as CISA requires; the sources do not name the specific patch or KB.

## Timeline

- 2026-10-23T19:11:52+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2011-2005
- 2026-10-23T19:13:45+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2011-2005
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2011-2005

## From the sources

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."

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_