CVE-2026-58530 — Windows Resilient File System (ReFS) Remote Code Execution Vulnerability

Executive Summary

Heap-based buffer overflow in Windows Resilient File System (ReFS) allows an unauthorized attacker to execute code locally.

Overview

7.8

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

Exploitation Unlikely

MS Exploit Likelihood

Category Remote Code Execution

Weakness CWE-122: Heap-based Buffer Overflow

Released Jul 14 2026

Last Updated Jul 14 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00338 — 0.26643 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

0.00338

probability of exploitation in the next 30 days

0.26643 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	`5099535 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1607 for x64-based Systems	`5099535 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1809 for 32-bit Systems	`5099538 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1809 for x64-based Systems	`5099538 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for x64-based Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for x64-based Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5101650 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 24H2 for x64-based Systems	`5101650 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5101650 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 25H2 for x64-based Systems	`5101650 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5101649 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 version 26H1 for x64-based Systems	`5101649 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2016	`5099535 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2016 (Server Core installation)	`5099535 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2019	`5099538 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2019 (Server Core installation)	`5099538 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2022	`5099540 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2025	`5099536 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2025 (Server Core installation)	`5099536 (Security Update)`	Important	Remote Code Execution	Yes

Patches

7 patches

Article	Type	Restart
`5099535`	Security Update	Yes
`5099538`	Security Update	Yes
`5099539`	Security Update	Yes
`5101650`	Security Update	Yes
`5101649`	Security Update	Yes
`5099540`	Security Update	Yes
`5099536`	Security Update	Yes

Patch Diff

ghidriff · refs.sys (KB5099540)

Kernel heap-based buffer overflow (CWE-122) in the Windows ReFS driver refs.sys checkpoint serialization, mount-time arbitrary code execution (Important, RCE, AV:L, UI:R, CVSS 7.8). A producer/consumer bug separated in time: a crafted ReFS checkpoint carries an excessive globalTableCount (DWORD at record + 0x90). PRE: CmsVolume::ValidateCheckpointRecord accepts the count as long as it is internally consistent with the INPUT record - the key check count <= size >> 2 && count > 4 bounds it only against the input checkpoint's own size (a larger crafted record raises the permitted count), plus offset-table-inside-record checks; nothing bounds it against the destination buffer. During mount, ReadLatestCheckpoint promotes it to persistent kernel state as volume + 478 = count - 13, losing its untrusted origin. Later CmsVolume::FormatCheckpointRecord restores count = volume[478] + 13 and writes that many offset-table entries and serialized roots into the fixed checkpoint record buffer with NO comparison of the final cursor against the buffer size - a kernel OOB write. Mounting a crafted ReFS image (AV:L, UI:R) reaches the path, yielding kernel code execution. Diff of refs.sys 10.0.20348.4893 -> .5386 (Jul 14 2026, KB5099540, Server 2022) confirms the fix: the formatter is logically unchanged (only relocated); the CVE-relevant delta is an ABSOLUTE count cap added to ValidateCheckpointRecord (ratio 0.37), gated behind CFR flags Feature_1337977145 / Feature_3102454072, rejecting the oversized globalTableCount before it is promoted to persistent state. Cross-checked against an independent writeup; functions (ValidateCheckpointRecord / FormatCheckpointRecord / ReadLatestCheckpoint) and offsets (+0x90 count, volume+478) match the ghidriff.

Pre-patch version 10.0.20348.4893 Download

Post-patch version 10.0.20348.5386 Download

Function	Address	Change	Note
`CmsVolume::ValidateCheckpointRecord`	`code change`	code (absolute globalTableCount cap added, CFR-gated)	Pre (ratio 0.37): globalTableCount at record+0x90 checked only as count <= size>>2 && count > 4 (input-record-relative) plus offset-table-inside-record checks - not bounded to the destination buffer. Post (Feature_1337977145 / Feature_3102454072): adds an absolute cap that rejects an oversized count before it is promoted to volume+478 and later consumed by the formatter.
`CmsVolume::FormatCheckpointRecord`	`sink (unchanged / relocated)`	note (the OOB-write sink; logically unchanged)	Restores count = volume[478] + 13 and serializes that many offset-table entries and roots into the fixed checkpoint buffer with no destination-size check. The formatter body is logically equivalent between builds (relocated); the fix is entirely in the validator.
`CmsVolume::ReadLatestCheckpoint`	`code change`	code (promotes the validated count to persistent state)	Stores volume + 478 = globalTableCount - 13 (extended-root count) during mount; the untrusted value's origin is lost here, then restored later by FormatCheckpointRecord.
`Feature_1337977145 / Feature_3102454072`	`gate`	added (CFR gates)	CFR flags gating the count cap in ValidateCheckpointRecord; the original record-local-only validation ships when disabled.

View full diff report View RCA report

Attack Path

A crafted ReFS checkpoint globalTableCount passes record-local validation, then overflows the destination checkpoint buffer during formatting

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

Donghyeon Oh
Jonghoi Kim
R4nger with Kunlun Lab & Zhiniang Peng with HUST

References

MSRC Advisory MITRE NVD