CVE-2025-49761 Overview
CVE-2025-49761 is a use-after-free vulnerability [CWE-416] in the Microsoft Windows Kernel. An authorized local attacker can exploit the flaw to elevate privileges on affected systems. The issue impacts every currently supported Windows client and server release, spanning Windows 10, Windows 11, and Windows Server 2008 through Windows Server 2025. Microsoft disclosed the issue through its August 2025 Patch Tuesday cycle.
Critical Impact
Successful exploitation grants attackers SYSTEM-level privileges on the target host, enabling full control over confidentiality, integrity, and availability of the affected Windows system.
Affected Products
- Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (22H2, 23H2, 24H2)
- Microsoft Windows Server 2008, 2012, 2012 R2, 2016, 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-08-12 - CVE-2025-49761 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-49761
Vulnerability Analysis
The vulnerability is a use-after-free condition [CWE-416] in the Windows Kernel. The kernel references a memory object after that object has been freed, allowing an attacker to influence the contents of the reclaimed allocation. When the kernel later dereferences the stale pointer, attacker-controlled data can be interpreted as a valid kernel structure.
The flaw requires low privileges and no user interaction. Exploitation is restricted to a local attack vector, meaning the adversary must already have code execution on the target host. Successful exploitation yields kernel-mode execution and full SYSTEM privileges. This provides a reliable pivot for post-compromise activity such as credential theft, security tool tampering, and persistence installation.
Root Cause
The root cause is improper object lifetime management in a kernel component. A kernel routine releases a memory allocation without invalidating outstanding references. Subsequent operations on the freed object trigger the unsafe reuse. Microsoft has not published low-level implementation details for the affected function.
Attack Vector
An authenticated local user runs a purpose-built binary that repeatedly invokes the vulnerable kernel path. The attacker sprays the kernel pool to reclaim the freed allocation with a controlled structure. When the kernel dereferences the dangling pointer, execution transfers into attacker-controlled code at ring 0. Chained with an initial access primitive such as phishing or a web browser exploit, this vulnerability enables sandbox escape and privilege escalation to SYSTEM.
No public proof-of-concept exploit is available at the time of writing. Refer to the Microsoft Security Update Guide for CVE-2025-49761 for vendor-supplied technical detail.
Detection Methods for CVE-2025-49761
Indicators of Compromise
- Unexpected user-mode processes spawning children that run as NT AUTHORITY\SYSTEM shortly after low-privilege execution.
- Kernel bugchecks or SYSTEM_SERVICE_EXCEPTION (0x3B) and KERNEL_MODE_HEAP_CORRUPTION (0x13A) crashes on hosts that were previously stable.
- New services, scheduled tasks, or driver loads created by non-administrative user contexts.
Detection Strategies
- Monitor Windows Event ID 4688 for process-creation chains where a medium-integrity parent produces a SYSTEM-integrity child without a valid elevation path.
- Correlate Sysmon Event ID 1 and 10 to flag suspicious process access to lsass.exe or csrss.exe following execution of unsigned binaries.
- Baseline kernel crash telemetry from WER and Event ID 1001 to surface repeated faults that indicate exploit attempts.
Monitoring Recommendations
- Ingest kernel and security event logs into a centralized SIEM for cross-host correlation of privilege escalation attempts.
- Track patch compliance for the August 2025 Windows security update across all affected client and server SKUs.
- Alert on newly installed kernel drivers or modifications to HKLM\SYSTEM\CurrentControlSet\Services originating from non-administrative sessions.
How to Mitigate CVE-2025-49761
Immediate Actions Required
- Apply the Microsoft August 2025 security update to all affected Windows client and server systems.
- Prioritize patching on multi-user hosts, terminal servers, and jump boxes where local access is broadly available.
- Audit local account membership and remove unnecessary interactive logon rights to reduce the attacker population.
Patch Information
Microsoft addressed the flaw in the August 2025 monthly security update. Refer to the Microsoft Security Update Guide for CVE-2025-49761 for the specific KB article per operating system build. Windows Server 2008 and 2012 fixes are delivered through Extended Security Updates.
Workarounds
- No vendor-supplied workaround exists; patching is the only supported remediation.
- Restrict local logon and Remote Desktop access to trusted administrative accounts until updates are deployed.
- Enforce application control policies such as Windows Defender Application Control to block unsigned exploit binaries from executing.
# Verify installed Windows updates and confirm the August 2025 patch is present
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Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
