CVE-2026-34343 — Windows Application Identity (AppID) Subsystem Elevation of Privilege Vulnerability

Executive Summary

Heap-based buffer overflow in Windows Application Identity (AppID) Subsystem allows an authorized attacker to elevate privileges locally.

Overview

7.8

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Elevation of Privilege

Weakness CWE-122: Heap-based Buffer Overflow

Released May 12 2026

Last Updated May 12 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00326 — 0.25371 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:U/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

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 6.8

EPSS Score

0.00326

probability of exploitation in the next 30 days

0.25371 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

23 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 Version 1607 for 32-bit Systems	`5087537 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1607 for x64-based Systems	`5087537 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for 32-bit Systems	`5087538 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for x64-based Systems	`5087538 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5087544 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5087544 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for x64-based Systems	`5087544 (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	`5087420 (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 5089549 (Security Update) 5089466 (Security Hotpatch Update) Important Elevation of Privilege 5082063 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.8457 10.0.26100.8390 Yes None Windows 11 Version 24H2 for x64-based Systems 5089549 (Security Update) 5089466 (Security Hotpatch Update) Important Elevation of Privilege 5082063 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.8457 10.0.26100.8390 Yes None Windows 11 Version 25H2 for ARM64-based Systems 5089549 (Security Update) 5089466 (Security Hotpatch Update) Important Elevation of Privilege 5083769 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26200.8457 10.0.26200.8390 Yes None Windows 11 Version 25H2 for x64-based Systems 5089549 (Security Update) 5089466 (Security Hotpatch Update) Important Elevation of Privilege 5083769 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26200.8457 10.0.26200.8390 Yes None Windows 11 Version 26H1 for ARM64-based Systems	`5089548 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 version 26H1 for x64-based Systems	`5089548 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2012	`5087470 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 (Server Core installation)	`5087470 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 R2	`5087471 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 R2 (Server Core installation)	`5087471 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2016	`5087537 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2016 (Server Core installation)	`5087537 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019	`5087538 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019 (Server Core installation)	`5087538 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022 5087545 (Security Update) 5087424 (Security Hotpatch Update) Important Elevation of Privilege 5082142 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.5139 10.0.20348.5074 Yes None Windows Server 2022 (Server Core installation) 5087545 (Security Update) 5087424 (Security Hotpatch Update) Important Elevation of Privilege 5082142 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.5139 10.0.20348.5074 Yes None Windows Server 2022, 23H2 Edition (Server Core installation)	`5087541 (Security Update)`	Important	Elevation of Privilege	Yes

Patches

10 patches

Article	Type	Restart
`5087537`	Security Update	Yes
`5087538`	Security Update	Yes
`5087544`	Security Update	Yes
`5094127`	Security Update	Yes
`5087420`	Security Update	Yes
`5093998`	Security Update	Yes
`5089548`	Security Update	Yes
`5087470`	Monthly Rollup	Yes
`5087471`	Monthly Rollup	Yes
`5087541`	Security Update	Yes

Patch Diff

ghidriff · appid.sys (KB5089549)

Integer-truncation heap buffer overflow (CWE-122) in the Windows Application Identity subsystem appid.sys (also srpapi.dll/appidapi.dll) AiConvertFullImagePathToMacroFormat, local EoP. The function rewrites a path prefix with macros (%OSDRIVE%/%REMOVABLE%/%HOT%). It computes the result length as a2->Length + prefix_len - matched_len where all three are USHORT UNICODE_STRING.Length fields; the 32-bit arithmetic result is stored back into a USHORT DestinationString.Length (explicit (unsigned __int16) cast in appid.sys), truncating to 16 bits. The truncated length is passed to AiAlloc as the buffer size, so a buffer far smaller than needed is allocated, while the subsequent memmove/memcpy copy uses the original non-truncated size -> heap/pool overflow (e.g. Length=65000, prefix=1000, matched=10 needs 65990 bytes but allocates 470 -> ~64520-byte overflow). The bug exists in two loops (macro-prefix array and the global ::P linked list). Diff of appid.sys 10.0.26100.8246 -> .8457 (May 12 2026, KB5089549) confirms the fix: gated behind CFR flag Feature_3858697530, a 32-bit intermediate length plus an explicit `> 0xFFFE` bound check are added before storing to the 16-bit field / allocating; over-length aborts with STATUS_NAME_TOO_LONG (0xC0000106). Applied to both loops; the global-list error path also frees P[1] only when independently allocated (P[1] != i[6]). Note: our diff shows Feature_3858697530 (build/arch); the >0xFFFE check and 32-bit widening are as described.

Pre-patch version 10.0.26100.8246 Download

Post-patch version 10.0.26100.8457 Download

Function	Address	Change	Note
`AiConvertFullImagePathToMacroFormat`	`code change`	code (32-bit length + >0xFFFE bound check, CFR-gated)	Pre: DestinationString.Length = (USHORT)(a2->Length + prefix_len - matched_len) truncates >0xFFFF lengths; AiAlloc sized to the truncated value while memmove/memcpy use the real size -> overflow. Post (Feature_3858697530): 32-bit intermediate; if 0xfffe < len return 0xC0000106 (STATUS_NAME_TOO_LONG) in both the macro-prefix loop and the global-list loop; conditional cleanup of P[1] (only if P[1] != i[6]).
`Feature_3858697530`	`gate`	added (CFR gate)	CFR flag gating the widened length + >0xFFFE bound; original truncating path still ships when disabled.

View full diff report View RCA report

Attack Path

A very long image path truncates to a 16-bit length that under-sizes the AiAlloc buffer, overflowed by the full-size copy

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

Erik Egsgard

References

MSRC Advisory MITRE NVD