CVE-2026-20875 Overview
CVE-2026-20875 is a null pointer dereference vulnerability in the Windows Local Security Authority Subsystem Service (LSASS) that allows an unauthorized attacker to cause a denial of service condition over a network. LSASS is a critical Windows system process responsible for enforcing security policy, handling user authentication, and managing Active Directory services. Exploitation of this vulnerability could result in system crashes or service disruptions affecting authentication services across affected Windows environments.
Critical Impact
Successful exploitation allows remote attackers to crash LSASS without authentication, potentially causing system-wide authentication failures and requiring system restarts to restore normal operations.
Affected Products
- Windows Local Security Authority Subsystem Service (LSASS)
- Windows operating systems with vulnerable LSASS implementations
Discovery Timeline
- 2026-01-13 - CVE-2026-20875 published to NVD
- 2026-01-13 - Last updated in NVD database
Technical Details for CVE-2026-20875
Vulnerability Analysis
This vulnerability stems from improper pointer handling within the LSASS process. When LSASS receives specially crafted network requests, the service fails to properly validate pointer references before dereferencing them. This results in a null pointer dereference condition (CWE-476) that causes the LSASS process to crash.
The attack can be conducted remotely over a network without requiring authentication, making it particularly dangerous in enterprise environments where LSASS handles domain authentication. When LSASS crashes, it triggers Windows' automatic recovery mechanisms, which typically result in a forced system restart to maintain system integrity.
Root Cause
The root cause is a null pointer dereference (CWE-476) in the LSASS service. The vulnerability occurs when the service processes certain network requests without adequately checking if pointer values are valid before attempting to access the memory locations they reference. This programming error allows attackers to trigger conditions where the code attempts to read or write to memory address zero, causing an immediate process crash.
Attack Vector
The vulnerability is exploitable over a network without requiring user interaction or prior authentication. An attacker can send malformed authentication or directory service requests to a target system's LSASS service. Since LSASS listens on network ports for legitimate authentication traffic, it provides an accessible attack surface. The attack requires low complexity to execute and does not require any privileges on the target system.
The exploitation mechanism involves crafting network packets that cause LSASS to enter a code path where null pointer validation is absent. When the vulnerable code path is triggered, LSASS attempts to dereference a null pointer, resulting in an access violation that terminates the process.
Detection Methods for CVE-2026-20875
Indicators of Compromise
- Unexpected LSASS process crashes or restarts recorded in Windows Event Logs
- Windows Error Reporting (WER) entries indicating lsass.exe access violations at null memory addresses
- Unusual network traffic patterns targeting LSASS-associated ports prior to system restarts
- Multiple authentication failures followed by system reboots in domain controller logs
Detection Strategies
- Monitor Windows System Event Log for Event ID 1000 (Application Error) and Event ID 1001 (Windows Error Reporting) entries related to lsass.exe
- Deploy network intrusion detection rules to identify malformed authentication protocol packets
- Configure endpoint detection solutions to alert on abnormal LSASS process terminations
- Implement baseline monitoring for LSASS memory consumption and process stability
Monitoring Recommendations
- Enable Windows Defender Exploit Guard to monitor LSASS process integrity
- Configure centralized logging for all domain controllers and authentication servers to correlate LSASS-related events
- Establish alerting thresholds for LSASS crash frequency that could indicate active exploitation attempts
- Monitor for unusual inbound network connections to authentication service ports
How to Mitigate CVE-2026-20875
Immediate Actions Required
- Apply the latest Windows security updates from Microsoft addressing CVE-2026-20875
- Implement network segmentation to restrict access to LSASS-associated ports from untrusted networks
- Enable Windows Defender Credential Guard where supported to provide additional LSASS protection
- Review and restrict firewall rules to limit network exposure of authentication services
Patch Information
Microsoft has released a security update to address this vulnerability. Refer to the Microsoft Security Advisory CVE-2026-20875 for detailed patch information, affected product versions, and download links. Organizations should prioritize patching domain controllers and systems providing authentication services.
Workarounds
- Restrict network access to LSASS ports using host-based firewalls or network ACLs to trusted systems only
- Deploy additional network-layer protection such as IPsec policies requiring authentication for connections to critical servers
- Consider enabling LSASS as a Protected Process Light (PPL) if not already configured to enhance process integrity
- Implement network monitoring to detect and block potential exploitation attempts while awaiting patch deployment
# Enable LSASS as Protected Process Light via Registry (requires reboot)
reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa" /v RunAsPPL /t REG_DWORD /d 1 /f
# Verify LSASS protection status after reboot
reg query "HKLM\SYSTEM\CurrentControlSet\Control\Lsa" /v RunAsPPL
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
