CVE-2025-29969: Windows 10 1507 Race Condition Flaw

CVE-2025-29969 Overview

CVE-2025-29969 is a Time-of-Check Time-of-Use (TOCTOU) race condition in Windows Fundamentals. An authorized attacker can exploit the race window to execute code over the network. The flaw is tracked under CWE-367 and affects a broad range of Microsoft Windows desktop and server editions, from Windows 10 1507 and Windows Server 2008 through Windows 11 24H2 and Windows Server 2025. Microsoft published the advisory on May 13, 2025 and released fixes through its monthly security update channel. The EPSS probability is 0.26% at the 49.378 percentile, and the vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog.

Critical Impact

An authenticated network attacker who wins the race condition can execute arbitrary code against the targeted Windows host, compromising confidentiality, integrity, and availability.

Affected Products

• Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2) and Windows 11 (22H2, 23H2, 24H2)
• Microsoft Windows Server 2008, 2012, 2012 R2, 2016, 2019
• Microsoft Windows Server 2022, Server 2022 23H2, and Server 2025

Discovery Timeline

• 2025-05-13 - CVE-2025-29969 published to NVD
• 2025-05-13 - Microsoft releases security update for CVE-2025-29969
• 2025-05-19 - Last updated in NVD database

Technical Details for CVE-2025-29969

Vulnerability Analysis

The vulnerability resides in Windows Fundamentals, a core operating system component shared across desktop and server editions. The issue is a TOCTOU race condition, classified under CWE-367. The component validates a resource state, then later acts on that state without re-checking. An attacker who modifies the resource between the check and the use can redirect the operation to attacker-controlled data or paths. The advisory describes the outcome as remote code execution by an authorized attacker, indicating the attacker requires valid network-accessible credentials or session context on the target.

Root Cause

The root cause is a non-atomic sequence between validation and use of a shared resource inside Windows Fundamentals. Because the check and the subsequent operation are separated in time, a concurrent thread or process can alter the underlying object — for example, a file, handle, or registry value — after validation succeeds but before it is consumed. Microsoft has not publicly disclosed the specific function or syscall affected. The high attack complexity reflects the timing precision required to win the race reliably.

Attack Vector

Exploitation requires network access and low-privilege authentication on the target system. The attacker initiates an operation that triggers the vulnerable code path, then races a parallel action to mutate the validated resource before Windows Fundamentals uses it. A successful race causes the component to operate on attacker-controlled input, leading to code execution in the security context of the vulnerable process. No user interaction is required.

No public proof-of-concept code is available. See the Microsoft Security Update Guide entry for CVE-2025-29969 for vendor technical details.

Detection Methods for CVE-2025-29969

Indicators of Compromise

• Unexpected child processes spawned by Windows Fundamentals-related system services on patched or unpatched hosts.
• Anomalous authenticated network sessions originating from low-privilege accounts that immediately trigger code execution behavior.
• High-frequency, repeated file or handle operations against the same resource within microseconds, consistent with race-window attempts.

Detection Strategies

• Monitor for authenticated remote sessions that rapidly issue parallel operations against identical kernel objects or files.
• Correlate Windows Security event IDs 4624 (logon) and 4688 (process creation) to identify post-authentication code execution from system components.
• Hunt for new or unusual binaries written to disk by SYSTEM-context processes immediately after a remote authentication event.

Monitoring Recommendations

• Enable Sysmon with Event IDs 1, 7, 11, and 13 to capture process, image load, and file create activity on Windows Fundamentals binaries.
• Forward Windows Defender Application Control and AppLocker audit logs to a central log store for retroactive hunting.
• Track patch deployment state of KB updates referenced in the Microsoft advisory across the fleet.

How to Mitigate CVE-2025-29969

Immediate Actions Required

• Apply the May 2025 Microsoft security updates referenced in the Microsoft Security Update Guide entry for CVE-2025-29969 to all affected Windows desktop and server editions.
• Prioritize patching internet-exposed and multi-user systems where authenticated network access is broadly available.
• Audit and reduce the number of accounts with network logon rights to limit the attacker population.

Patch Information

Microsoft released fixes for CVE-2025-29969 in the May 13, 2025 security update cycle. Updates are available for Windows 10 (1507, 1607, 1809, 21H2, 22H2), Windows 11 (22H2, 23H2, 24H2), and Windows Server 2008 through Windows Server 2025. Refer to the Microsoft Security Update Guide for the specific KB article matching each operating system build.

Workarounds

• Restrict network reachability of affected hosts using host-based firewall rules and network segmentation until patches are applied.
• Enforce least privilege on service accounts and require multi-factor authentication for remote logons to reduce the pool of authorized attackers.
• Disable unused remote management protocols and services on Windows Fundamentals-dependent hosts to shrink the attack surface.

# Configuration example - verify patch status on Windows hosts using PowerShell
Get-HotFix | Where-Object { $_.InstalledOn -ge (Get-Date '2025-05-13') } | Sort-Object InstalledOn -Descending