CVE-2025-27478 Overview
CVE-2025-27478 is a heap-based buffer overflow vulnerability in the Windows Local Security Authority (LSA) subsystem. An authorized local attacker can exploit the flaw to elevate privileges on affected Windows client and server operating systems. The vulnerability is tracked under CWE-122 (Heap-based Buffer Overflow) and impacts confidentiality, integrity, and availability once successfully exploited. Microsoft published the advisory on April 8, 2025, covering supported Windows 10, Windows 11, and Windows Server releases from Server 2008 through Server 2025.
Critical Impact
Successful exploitation grants SYSTEM-level privileges on the local host, giving an attacker full control over the operating system, credentials cached by LSA, and any security policy enforcement.
Affected Products
- Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (versions 22H2, 23H2, 24H2)
- Microsoft Windows Server 2008, 2012, 2016, 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-04-08 - CVE-2025-27478 published to the National Vulnerability Database (NVD)
- 2025-04-08 - Microsoft released the security update via the Microsoft Security Update for CVE-2025-27478
- 2026-06-17 - Last updated in the NVD database
Technical Details for CVE-2025-27478
Vulnerability Analysis
The vulnerability resides in the Windows Local Security Authority (LSA), the subsystem responsible for enforcing security policy, authenticating users, and managing local security tokens. A heap-based buffer overflow occurs when LSA processes attacker-influenced data without properly validating the destination buffer size on the heap. Because LSA runs in a highly privileged security context, an attacker who successfully corrupts heap memory can influence execution flow and gain SYSTEM privileges.
Exploitation requires local access and low-privileged authenticated execution on the target host. Microsoft classifies the attack complexity as high, indicating the attacker must win a specific condition or manipulate memory layout to reliably trigger the overflow. The vulnerability provides a path from a standard user account to full local administrative control.
Root Cause
The root cause is improper bounds checking on a heap allocation inside LSA request handling logic. When the affected routine copies data into a heap buffer, it fails to validate that the source length remains within the allocated destination. The resulting out-of-bounds write corrupts adjacent heap structures, which an attacker can shape to overwrite function pointers or object metadata used by LSA.
Attack Vector
The attack vector is local. An attacker must first obtain code execution as a low-privileged user, for example through phishing, credential theft, or a foothold gained by other means. From that account, the attacker issues crafted requests to LSA that trigger the vulnerable code path. No user interaction is required beyond the attacker's own authenticated session. Microsoft has not reported active exploitation, and the CVE is not listed on the CISA Known Exploited Vulnerabilities catalog. Technical proof-of-concept code is not publicly available at the time of publication. See the Microsoft Security Update for CVE-2025-27478 for vendor details.
Detection Methods for CVE-2025-27478
Indicators of Compromise
- Unexpected crashes or restarts of the lsass.exe process, or Windows Error Reporting entries referencing LSA heap corruption.
- New or unexpected local administrator accounts, service installations, or scheduled tasks appearing shortly after a standard-user logon.
- Anomalous handle opens to lsass.exe from non-system processes preceding privilege changes on the host.
Detection Strategies
- Monitor Windows Security event logs for privilege escalation patterns, including Event ID 4672 (special privileges assigned) issued to previously unprivileged users.
- Correlate lsass.exe crash telemetry (Event ID 1000 in Application logs) with subsequent process creation events under SYSTEM.
- Hunt for local user-to-SYSTEM transitions that are not explained by an installer, service start, or scheduled task from a signed binary.
Monitoring Recommendations
- Ingest endpoint process, image load, and crash telemetry into a centralized analytics platform to baseline normal LSA behavior.
- Alert on any user-mode process attempting to write to lsass.exe memory or opening it with PROCESS_VM_WRITE rights.
- Track patch compliance for the April 2025 cumulative updates across all Windows and Windows Server assets.
How to Mitigate CVE-2025-27478
Immediate Actions Required
- Apply the April 2025 Microsoft security updates referenced in the Microsoft Security Update for CVE-2025-27478 to all affected Windows client and server systems.
- Prioritize domain controllers, jump hosts, and any multi-user servers where LSA compromise would yield broad credential exposure.
- Reduce the pool of interactive users on sensitive systems and enforce least privilege for standard accounts.
Patch Information
Microsoft addressed CVE-2025-27478 in the April 8, 2025 security update cycle. Administrators should install the cumulative update matching their Windows build using Windows Update, Windows Server Update Services (WSUS), or Microsoft Update Catalog. Full patch mapping per build is available in the Microsoft Security Update for CVE-2025-27478.
Workarounds
- Microsoft has not published a supported workaround; patching is the required remediation path.
- Enable LSA protection (RunAsPPL) to raise the barrier for tampering with lsass.exe while patch deployment is in progress.
- Restrict local logon rights and enforce application allowlisting to limit which binaries a low-privileged attacker can execute on affected hosts.
# Enable LSA Protection (RunAsPPL) to harden lsass.exe
# Run in an elevated PowerShell session, then reboot
New-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa" `
-Name "RunAsPPL" -Value 1 -PropertyType DWord -Force
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
