CVE-2026-47291 — HTTP.sys Remote Code Execution Vulnerability

Executive Summary

Integer overflow or wraparound in Windows HTTP.sys allows an unauthorized attacker to execute code over a network.

Overview

9.8

CVSS CRITICAL

Critical

MS Severity

Not Exploited

MS Exploit Status

More Likely

MS Exploit Likelihood

Category Remote Code Execution

Weakness CWE-190: Integer Overflow or Wraparound

Released Jun 9 2026

Last Updated Jun 9 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.2275 — 0.97522 percentile

NVD CVSS 9.8 CRITICAL — matches MSRC

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

ATTACK VECTOR

Network

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

None

USER INTERACTION

None

SCOPE

Unchanged

CONFIDENTIALITY

High

INTEGRITY

High

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 8.5

EPSS Score

0.2275

probability of exploitation in the next 30 days

0.97522 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

30 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 Version 1607 for 32-bit Systems	`5094122 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 1607 for x64-based Systems	`5094122 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 1809 for 32-bit Systems	`5094123 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 1809 for x64-based Systems	`5094123 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5094127 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5094127 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 21H2 for x64-based Systems	`5094127 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5094127 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5094127 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 10 Version 22H2 for x64-based Systems	`5094127 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 11 Version 23H2 for ARM64-based Systems	`5093998 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 11 Version 23H2 for x64-based Systems	`5093998 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5094126 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 11 Version 24H2 for x64-based Systems	`5094126 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5094126 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 11 Version 25H2 for x64-based Systems	`5094126 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5095051 (Security Update)`	Critical	Remote Code Execution	Yes
Windows 11 version 26H1 for x64-based Systems	`5095051 (Security Update)`	Critical	Remote Code Execution	Yes
Windows Server 2012	`5094042 (Monthly Rollup)`	Critical	Remote Code Execution	Yes
Windows Server 2012 (Server Core installation)	`5094042 (Monthly Rollup)`	Critical	Remote Code Execution	Yes
Windows Server 2012 R2	`5094041 (Monthly Rollup)`	Critical	Remote Code Execution	Yes
Windows Server 2012 R2 (Server Core installation)	`5094041 (Monthly Rollup)`	Critical	Remote Code Execution	Yes
Windows Server 2016	`5094122 (Security Update)`	Critical	Remote Code Execution	Yes
Windows Server 2016 (Server Core installation)	`5094122 (Security Update)`	Critical	Remote Code Execution	Yes
Windows Server 2019	`5094123 (Security Update)`	Critical	Remote Code Execution	Yes
Windows Server 2019 (Server Core installation)	`5094123 (Security Update)`	Critical	Remote Code Execution	Yes
Windows Server 2022	`5094128 (Security Update)`	Critical	Remote Code Execution	Yes
Windows Server 2022 (Server Core installation)	`5094128 (Security Update)`	Critical	Remote Code Execution	Yes
Windows Server 2025	`5094125 (Security Update)`	Critical	Remote Code Execution	Yes
Windows Server 2025 (Server Core installation)	`5094125 (Security Update)`	Critical	Remote Code Execution	Yes

Patches

10 patches

Article	Type	Restart
`5094122`	Security Update	Yes
`5094123`	Security Update	Yes
`5094127`	Security Update	Yes
`5093998`	Security Update	Yes
`5094126`	Security Update	Yes
`5095051`	Security Update	Yes
`5094042`	Monthly Rollup	Yes
`5094041`	Monthly Rollup	Yes
`5094128`	Security Update	Yes
`5094125`	Security Update	Yes

Patch Diff

ghidriff · http.sys (KB5060842)

Remote, pre-auth kernel pool overflow (CWE-190 -> CWE-122) in HTTP.sys HTTP/1.x header parsing. UlpParseNextRequest tracks receive buffers in a per-request buffer-reference array with 16-bit capacity (+0x640) and count (+0x642) fields. When count reaches capacity it grows the array: ExAllocatePool3(0x28 + capacity*8), memmove(count<<3), then capacity += 5 as a 16-bit add WITH NO OVERFLOW CHECK. After 13,107 growths capacity=0xFFFB; +5 = 0x10000 truncates to 0. The next reference forces a grow that allocates only 0x28+0*8 = 40 bytes but memmoves count<<3 (~524,256 bytes) -> ~500KB NonPagedPool overflow. Reachable only over HTTP/1.x-over-TLS: SChannel delivers each TLS record as a separate buffer (1:1 record->reference), so an attacker sends one header line per TLS record; plaintext HTTP coalesces and cannot climb the count. Needs MaxRequestBytes >= 262144 (non-default). IN-HOUSE ghidriff diff of 10.0.26100.8521 -> .8655 confirms the ZDI/TrendAI root cause exactly and reveals the fix: the growth logic is extracted into a new routine UlpReferenceBuffers that adds new=capacity+5; if (new < capacity) bail - the missing 16-bit overflow check. The fix is GATED behind a Known Issue Rollback global UxKirRefBufferOverflowCheck: when that byte is 0 the patched binary runs the ORIGINAL unchecked growth path, so file version alone does not determine patch state. Credit: MSRC haowei yan, goodbyeselene (@ynwarcs); public analysis Yazhi Wang & Jonathan Lein (TrendAI/ZDI).

Pre-patch version 10.0.26100.8521 Download

Post-patch version 10.0.26100.8655 Download

Function	Address	Change	Note
`UlpParseNextRequest`	`pre: inline growth (calls memmove) -> post: calls UlpReferenceBuffers`	code (vulnerable inline growth removed, replaced by call to fixed routine)	Pre-patch inlines the buffer-ref array growth: ExAllocatePool3(0x28 + (ushort)(state+0x640)8), memmove((ushort)(state+0x642) << 3), (short*)(state+0x640) += 5 with no overflow check. Post-patch the inline block is replaced by cVar4 = UlpReferenceBuffers(state, buffer). Match 80%; loses direct memmove/ExAllocatePool3, gains UlpReferenceBuffers in its called-list.
`UlpReferenceBuffers`	`140097880 (effectively new; ghidriff mis-matched to WPP_SF_qII at 21%)`	added (extracted, bounds-checked growth routine; KIR-gated)	New routine holding the growth logic. Branches on global UxKirRefBufferOverflowCheck: if 0, runs the ORIGINAL vulnerable path (0x28 + capacity*8 alloc, capacity += 5, no check); if non-zero, computes uVar6 = capacity + 5, `if (uVar6 < capacity) goto bail` (16-bit overflow guard), allocates uVar6<<3, memmoves count<<3, stores the checked capacity. Both paths ship in .8655.

View full diff report View RCA report

Attack Path

One HTTP header line per TLS record overflows a 16-bit array-capacity counter, desyncing a 40-byte allocation from a ~500KB memmove in the kernel

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

No known exploits have been linked for this CVE yet. When available, exploit references will be sourced from public repositories and may be unverified, incomplete, or non-functional. Always review code carefully before use in any environment.

Acknowledgments

Microsoft
haowei yan
goodbyeselene

References

MSRC Advisory MITRE NVD