Introduction
A critical race condition vulnerability, CVE-2025-29969, has emerged within Windows Fundamentals, posing a significant threat to network-exposed Windows environments. This TOCTOU flaw enables authorized attackers to execute arbitrary code remotely, potentially leading to severe compromise of affected systems.
Affected Systems and Versions
- Windows 10 (all editions)
- Windows 11 (all editions)
- Windows Server 2016 through 2025
Systems with network exposure, particularly those utilizing SMB or RPC services, are vulnerable.
Technical Information
The core issue is a TOCTOU race condition, classified under CWE-367. The vulnerability occurs due to improper synchronization between resource validation and usage phases. Specifically:
- Check Phase: Windows Fundamentals validates a resource (e.g., file handle, network socket).
- Race Window: The attacker modifies the resource, typically by replacing a legitimate file or handle with a malicious one.
- Use Phase: Windows executes the altered resource, enabling arbitrary code execution.
Attack vectors primarily involve network-based exploitation through crafted RPC or SMB requests, making this vulnerability particularly dangerous for remotely accessible systems.
Patch Information
Microsoft has addressed this vulnerability in the May 2025 security update. Users should immediately apply:
- KB5058392 (Windows 10 and 11)
- KB5058411 (Windows Server 2016–2025)
Patch downloads and detailed instructions are available on the Microsoft Security Response Center.
Detection Methods
To detect potential exploitation:
- Monitor Windows Event Logs for Event ID 4673, indicating privilege escalation attempts.
- Observe network traffic for abnormal RPC or SMB requests targeting privileged ports (135, 445).
- Investigate unusual child processes spawned by
svchost.exe.
Vendor Security History
Microsoft has previously encountered similar TOCTOU vulnerabilities, notably CVE-2025-29824, exploited by ransomware groups. Despite rapid patch deployment, recurring vulnerabilities in legacy components remain a challenge.
