Proof-of-Concept Released for Windows ALPC Privilege Escalation via Error Reporting
A high-severity local privilege escalation (LPE) vulnerability, identified as CVE-2026-20817, has been publicly documented following the release of a proof-of-concept (PoC) exploit.
A high-severity local privilege escalation (LPE) vulnerability, identified as CVE-2026-20817, has been publicly documented following the release of a proof-of-concept (PoC) exploit.
Discovered in the Windows Error Reporting (WER) service, the flaw allows an authenticated, low-privileged user to execute arbitrary code with SYSTEM-level access.
Feature Details
CVE ID CVE-2026-20817
Severity Score CVSS 7.8 (High)
Target Component Windows Error Reporting (WER) Service
Attack Vector Local Privilege Escalation (ALPC)
Privilege Impact Low-Privilege User to SYSTEM Access
Patch Status Patched (January 2026 Security Update)
The vulnerability is rooted in how the Windows Error Reporting service manages advanced local procedure calls (ALPC) for interprocess communication.
The PoC, published by security researcher @bytecodevm (GitHub: @oxfemale) , demonstrates the severe risks of improper permission validation within core Windows communication mechanisms.
The vulnerability is rooted in how the Windows Error Reporting service manages advanced local procedure calls (ALPC) for interprocess communication.
Specifically, the SvcElevatedLaunch method (0x0D) fails to adequately validate the privileges of the calling application before executing commands.
An attacker leverages this oversight by generating a shared memory segment that houses a malicious command-line payload.
By connecting to the \WindowsErrorReportingService ALPC port and sending a specially crafted message, containing the client process ID, the shared memory handle, and the payload's length, the attacker manipulates the system.
The WER service duplicates the provided handle and initiates WerFault.exe , injecting the attacker's supplied command-line parameters directly from the shared memory block.
Because the WER service operates with highly elevated administrative rights, the maliciously spawned WerFault.exe process automatically inherits a SYSTEM token.
This token grants the attacker capabilities, including SeDebugPrivilege (enabling debugging of any process) and SeImpersonatePrivilege (allowing impersonation of any user).
Although the spawned token restricts SeTcbPrivilege (Act as part of the operating system), the acquired privileges remain sufficient for dumping credentials, installing persistent backdoors, or orchestrating a complete system takeover.
This vulnerability impacts a wide range of operating systems, including unpatched versions of Windows 10, Windows 11, Windows Server 2019, and Windows Server 2022.
Microsoft successfully patched CVE-2026-20817 in the January 2026 security updates by implementing enhanced validation checks within SvcElevatedLaunch to reject malicious process requests.
Organizations must deploy these updates across all Windows environments to secure their infrastructure.
If immediate patching is unfeasible, administrators can temporarily disable the service using the command sc config WerSvc start=disabled and sc stop WerSvc .
Security operations centers should actively hunt for anomalies using Security Event ID 4688 to detect WerFault.exe executing unusual command lines, and Sysmon Event ID 10 to spot irregular SYSTEM token behaviors.
Applying these proactive defense strategies will significantly disrupt privilege escalation attempts.
Based on reporting by GBHackers.