CVE-2026-41108 — Windows DNS Client Elevation of Privilege Vulnerability

Executive Summary

Heap-based buffer overflow in Microsoft Windows DNS allows an authorized attacker to elevate privileges locally.

Overview

7

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

Exploitation Unlikely

MS Exploit Likelihood

Category Elevation of Privilege

Weakness CWE-122: Heap-based Buffer Overflow

Released Jun 9 2026

Last Updated Jun 9 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00274 — 0.1967 percentile

NVD CVSS 7 HIGH — matches MSRC

CVSS Vector

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

ATTACK VECTOR

Local

ATTACK COMPLEXITY

High

PRIVILEGES REQUIRED

Low

USER INTERACTION

None

SCOPE

Unchanged

CONFIDENTIALITY

High

INTEGRITY

High

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 6.1

EPSS Score

0.00274

probability of exploitation in the next 30 days

0.1967 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)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1607 for x64-based Systems	`5094122 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for 32-bit Systems	`5094123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for x64-based Systems	`5094123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for x64-based Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for x64-based Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 23H2 for ARM64-based Systems	`5093998 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 23H2 for x64-based Systems	`5093998 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5094126 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for x64-based Systems	`5094126 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5094126 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 25H2 for x64-based Systems	`5094126 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5095051 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 version 26H1 for x64-based Systems	`5095051 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2012	`5094042 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 (Server Core installation)	`5094042 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 R2	`5094041 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 R2 (Server Core installation)	`5094041 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2016	`5094122 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2016 (Server Core installation)	`5094122 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019	`5094123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019 (Server Core installation)	`5094123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022	`5094128 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022 (Server Core installation)	`5094128 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025	`5094125 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025 (Server Core installation)	`5094125 (Security Update)`	Important	Elevation of Privilege	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 · dnsapi.dll (KB5094126)

Heap-based buffer overflow (CWE-122) in the Windows DNS client dnsapi.dll, local elevation of privilege to SYSTEM (Important, AV:L, AC:H race, CVSS 7.0). Dns_WriteStringToPacket(write_ptr, end_ptr, string, flag) serialises a name/label into the DNS packet buffer as a length-prefixed string. PRE: once the computed length passed the < 0x100 check, the function wrote the one-byte length prefix *write_ptr = (char)len BEFORE verifying that write_ptr was still inside the buffer (write_ptr < end_ptr). When the write pointer had already reached end_ptr, that length-prefix store landed one byte past the heap-allocated packet buffer - a one-byte heap overflow, reached by winning a race on the buffer state (MSRC AC:H). Because the DNS client runs in a service context, a successful overflow yields SYSTEM. Diff of dnsapi.dll 10.0.26100.8521 -> .8655 (Jun 9 2026, KB5094126) shows a single code-changed function, Dns_WriteStringToPacket: gated behind CFR flag Feature_3831740731, the fix adds a write_ptr < end_ptr precondition around the whole prefix-write-and-copy block ((feature == 0) || (write_ptr < end_ptr)), so the length byte can no longer be written at or past the buffer end; the boundary case now returns ERROR_BUFFER_OVERFLOW (0xea).

Pre-patch version 10.0.26100.8521 Download

Post-patch version 10.0.26100.8655 Download

Function	Address	Change	Note
`Dns_WriteStringToPacket`	`code change`	code (length-prefix write now bounds-guarded, CFR-gated)	Pre: *write_ptr = (char)len executed whenever len < 0x100, before checking write_ptr < end_ptr - a one-byte OOB heap write at the buffer boundary. Post (Feature_3831740731): adds ((feature == 0) \|\| (write_ptr < end_ptr)) precondition around the length-prefix store and the subsequent memcpy/Dns_StringCopy; boundary case falls through to ERROR_BUFFER_OVERFLOW.
`Feature_3831740731`	`gate`	added (CFR gate)	CFR flag gating the write_ptr < end_ptr bounds check in Dns_WriteStringToPacket; the original unconditional length-prefix write still ships when the flag is disabled.

View full diff report View RCA report

Attack Path

A length-prefix byte is written past the DNS packet buffer end, overflowing the heap by one byte

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.

Exploits & PoC

No public exploit or PoC has been linked for this CVE yet. When available, references are sourced from public repositories and may be unverified or non-functional — review carefully before use.

Detection Rules

No public Sigma or Nuclei detection rule has been mapped to this CVE yet. Coverage is concentrated on exploited / high-profile vulnerabilities; check SigmaHQ for updates.

Acknowledgments

WARP team at Microsoft

References

MSRC Advisory MITRE NVD