OnlyPatch
Windows Ancillary Function Driver for WinSock

CVE-2024-38193 — Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

Important CVSS 7.8 EPSS 0.27358 ⚠️ Exploited in the wild 🔬 Patch diffed 2024-08 archive

Executive Summary

None

Overview

7.8
CVSS HIGH
Important
MS Severity
Exploited
MS Exploit Status
Exploitation Detected
MS Exploit Likelihood
Category Elevation of Privilege
Weakness CWE-416: Use After Free
Released Aug 13 2024
Last Updated Aug 13 2024
Publicly Disclosed No
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.27358 — 0.97885 percentile
NVD CVSS 7.8 HIGH — matches MSRC

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
ATTACK VECTOR
Local
ATTACK COMPLEXITY
Low
PRIVILEGES REQUIRED
Low
USER INTERACTION
None
SCOPE
Unchanged
CONFIDENTIALITY
High
INTEGRITY
High
AVAILABILITY
High
EXPLOIT CODE MATURITY
Functional
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 7.2

EPSS Score

0.27358
probability of exploitation in the next 30 days
0.97885 percentile - updated 2026-08-14
View on FIRST.org

Affected Products

31 affected products
Product KB Article Severity Impact Restart Required
Windows 10 for 32-bit Systems 5041782 (Security Update) Important Elevation of Privilege Yes
Windows 10 for x64-based Systems 5041782 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1607 for 32-bit Systems 5041773 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1607 for x64-based Systems 5041773 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for 32-bit Systems 5041578 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for x64-based Systems 5041578 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for 32-bit Systems 5041580 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for ARM64-based Systems 5041580 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for x64-based Systems 5041580 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for 32-bit Systems 5041580 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for ARM64-based Systems 5041580 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for x64-based Systems 5041580 (Security Update) Important Elevation of Privilege Yes
Windows 11 version 21H2 for ARM64-based Systems 5041592 (Security Update) Important Elevation of Privilege Yes
Windows 11 version 21H2 for x64-based Systems 5041592 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 22H2 for ARM64-based Systems 5041585 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 22H2 for x64-based Systems 5041585 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 23H2 for ARM64-based Systems 5041585 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 23H2 for x64-based Systems 5041585 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 24H2 for ARM64-based Systems 5041571 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 24H2 for x64-based Systems 5041571 (Security Update) Important Elevation of Privilege Yes
Windows Server 2008 for 32-bit Systems Service Pack 2 5041850 (Monthly Rollup) 5041847 (Security Only) Important Elevation of Privilege 5040499 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C 6.0.6003.22825 Yes 5041850 5041847 Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 5041850 (Monthly Rollup) 5041847 (Security Only) Important Elevation of Privilege 5040499 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C 6.0.6003.22825 Yes 5041850 5041847 Windows Server 2008 for x64-based Systems Service Pack 2 5041850 (Monthly Rollup) 5041847 (Security Only) Important Elevation of Privilege 5040499 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C 6.0.6003.22825 Yes 5041850 5041847 Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 5041850 (Monthly Rollup) 5041847 (Security Only) Important Elevation of Privilege 5040499 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C 6.0.6003.22825 Yes 5041850 5041847 Windows Server 2008 R2 for x64-based Systems Service Pack 1 5041838 (Monthly Rollup) 5041823 (Security Only) Important Elevation of Privilege 5040497 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C 6.1.7601.27277 Yes 5041838 Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 5041838 (Monthly Rollup) 5041823 (Security Only) Important Elevation of Privilege 5040497 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C 6.1.7601.27277 Yes 5041838 Windows Server 2012 5041851 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 (Server Core installation) 5041851 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 R2 5041828 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 R2 (Server Core installation) 5041828 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2016 5041773 (Security Update) Important Elevation of Privilege Yes
Windows Server 2016 (Server Core installation) 5041773 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 5041578 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 (Server Core installation) 5041578 (Security Update) Important Elevation of Privilege Yes
Windows Server 2022 5041160 (Security Update) Important Elevation of Privilege Yes
Windows Server 2022 (Server Core installation) 5041160 (Security Update) Important Elevation of Privilege Yes
Windows Server 2022, 23H2 Edition (Server Core installation) 5041573 (Security Update) Important Elevation of Privilege Yes

Patches

11 patches
Article Type Restart
5041782 Security Update Yes
5041773 Security Update Yes
5041578 Security Update Yes
5041580 Security Update Yes
5041592 Security Update Yes
5041585 Security Update Yes
5041571 Security Update Yes
5041851 Monthly Rollup Yes
5041828 Monthly Rollup Yes
5041160 Security Update Yes
5041573 Security Update Yes

Patch Diff

ghidriff (VersionTrackingDiff, PDB symbols) · afd.sys (KB5041585)

Use-after-free in the Registered I/O (RIO) buffer cache (CVE-2024-38193, exploited ITW by Lazarus Group). Race condition between AfdRioGetAndCacheBuffer (_InterlockedIncrement on RIOBuffer.RefCount during cache fill) and AfdRioDereferenceBuffer (non-atomic RefCount==1 check + ExFreePool). Patch: AfdRioDereferenceBuffer uses atomic decrement with underflow bugcheck, AfdRioGetAndCacheBuffer calls new AfdRioReferenceBuffer for safe acquire, RIOBuffer.RefCount widened to 64-bit. All gated by CFR Feature_3168083257 + Feature_3695514937.

Pre-patch version 10.0.22621.3672 Download
Post-patch version 10.0.22621.4036 Download
Function Address Change Note
AfdRioDereferenceBuffer code (ratio 0.48, significant rewrite) Non-atomic RefCount==1 check replaced with atomic decrement + underflow guard (swi(0x29) bugcheck). RefCount widened to 64-bit. Gated by Feature_3168083257 / Feature_3695514937 (Feature_AfdRioCachedBuffer_IsEnabled).
AfdRioGetAndCacheBuffer code (ratio 0.48, significant rewrite) Raw _InterlockedIncrement(&RefCount) replaced with call to new AfdRioReferenceBuffer — returns NULL if buffer already freed, eliminating the TOCTOU window.
AfdRioReferenceBuffer (added) added function New atomic reference-acquire: checks IsInvalid and atomically increments RefCount only if buffer is still alive, returns 0 on failure.
AfdRioGetCachedBuffer code Cache hit/miss dispatcher, calls AfdRioGetAndCacheBuffer on miss.
AfdRioEvictCachedBuffer code (ratio 0.70) Cache eviction path updated to match new RIOBuffer layout.
AfdRioCreateRegisteredBuffer code (ratio 0.95) RIOBuffer allocation updated for wider structure (IsInvalid +0x18→+0x24, RefCount 32→64-bit at +0x18).
AfdRioInvalidateBuffer code (ratio 0.96) IsInvalid field access updated for new offset.
View full diff report View RCA report Download PoC

Attack Path

Use-after-free in the AFD Registered I/O buffer cache - a non-atomic refcount check races the cache-fill increment. Exploited in the wild by Lazarus Group.

Attack path for CVE-2024-38193 Use-after-free in the AFD Registered I/O buffer cache - a non-atomic refcount check races the cache-fill increment. Exploited in the wild by Lazarus Group. Attacker thread A RIO buffer cache RIOBuffer (0x20, 'RIOb') Attacker thread B RIORegisterBuffer(buf, len) - AfdRioCreateRegisteredBuffer 1 Acquires the write spinlock, finds a free slot in ArrayBuffers[], ExAllocatePool2(NonPaged, 0x20, 'RIOb'), sets RIOBuffer.RefCount = 1, releases the lock. Any unprivileged user; Winsock RIO needs no special rights. Thread A: RIOSend/RIOReceive -> AfdRioGetAndCacheBuffer(id) on cache miss 2 [A] v5 = ArrayBuffers[id] [B] if (!v5 || v5->IsInvalid) return NULL 3 The pointer is read and the validity flag checked, but nothing holds a reference yet. Thread B: AfdRioDereferenceBuffer sees RefCount == 1 and calls ExFreePool 4 The pre-patch check is a plain read-compare, not an atomic decrement. It can observe 1 in the window between Thread A's [B] and [C] and free the buffer out from under it. [C] _InterlockedIncrement(&v5->RefCount) on the freed block 5 Thread A increments a refcount inside pool memory that Thread B has already returned. The buffer then stays in CachedBufferArrays[] and is used for subsequent send/receive. Freed 0x20-byte NonPaged 'RIOb' block used as a live buffer descriptor 6 Patch: AfdRioDereferenceBuffer uses an atomic decrement with an underflow bugcheck, AfdRioGetAndCacheBuffer acquires via the new AfdRioReferenceBuffer, and RefCount widens to 64-bit. Gated behind Feature_3168083257 and Feature_3695514937.

Derived from the patch delta: the checks added by the vendor identify which fields crossed a trust boundary unvalidated. Reachability and privilege are taken from the call chain in the RCA report.

Known Exploits

Acknowledgments

Luigino Camastra and Milánek with Gen Digital

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