CVE-2022-26915: Windows 10 Secure Channel DoS Vulnerability

CVE-2022-26915 Overview

CVE-2022-26915 is a Denial of Service (DoS) vulnerability affecting the Windows Secure Channel (Schannel) security package. Schannel is a critical Security Support Provider (SSP) that implements SSL/TLS protocols for secure network communications in Windows. This vulnerability allows a remote, unauthenticated attacker to disrupt the availability of affected Windows systems by exploiting weaknesses in the Secure Channel component's handling of network requests.

Critical Impact

Remote attackers can cause system unavailability without authentication, potentially disrupting critical network services and secure communications across enterprise Windows environments.

Affected Products

• Microsoft Windows 10 (all versions including 20H2, 21H1, 21H2, 1607, 1809, 1909)
• Microsoft Windows 11 (x64 and ARM64)
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1
• Microsoft Windows RT 8.1
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and R2
• Microsoft Windows Server 2016 (including 20H2)
• Microsoft Windows Server 2019
• Microsoft Windows Server 2022

Discovery Timeline

• April 15, 2022 - CVE-2022-26915 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-26915

Vulnerability Analysis

The Windows Secure Channel (Schannel) is responsible for authenticating Windows hosts and encrypting data using SSL/TLS protocols. This vulnerability exists due to improper handling of certain network requests within the Schannel component. When exploited, the vulnerability causes the affected system to become unresponsive or crash, resulting in a denial of service condition.

The attack can be launched remotely over the network without requiring any user interaction or authentication. While the vulnerability does not compromise data confidentiality or integrity, the impact on availability is significant, particularly for systems providing critical network services that rely on secure communications.

Root Cause

The root cause of CVE-2022-26915 relates to improper resource handling within the Windows Secure Channel implementation. When processing specially crafted network requests targeting the SSL/TLS handshake or session management functions, the Schannel component fails to properly validate or limit resource consumption, leading to system instability or service disruption.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no prior access to the target system. An attacker can exploit this vulnerability by:

1. Identifying a target Windows system with exposed Secure Channel services (typically via HTTPS, LDAPS, or other TLS-protected protocols)
2. Sending specially crafted network packets designed to trigger the vulnerability in the Schannel component
3. Causing the target system to experience resource exhaustion or crash, resulting in denial of service

The vulnerability affects any service that utilizes Windows Schannel for TLS/SSL communications, including web servers, Active Directory services, and custom applications using Windows secure communication APIs.

Detection Methods for CVE-2022-26915

Indicators of Compromise

• Unexpected system crashes or service restarts affecting TLS-enabled services
• Abnormal network traffic patterns targeting ports commonly used for SSL/TLS communications (443, 636, etc.)
• Windows Event Log entries indicating Schannel errors or failures
• Increased memory or CPU consumption in lsass.exe or services utilizing Schannel

Detection Strategies

• Monitor Windows Event Logs for Schannel-related error events (Event ID 36888, 36871, or similar)
• Implement network intrusion detection rules to identify malformed SSL/TLS handshake attempts
• Deploy endpoint detection solutions capable of identifying abnormal Schannel behavior
• Use SentinelOne's behavioral AI to detect anomalous service terminations and resource exhaustion patterns

Monitoring Recommendations

• Enable verbose logging for Schannel operations via Windows registry settings
• Configure alerting for repeated service restarts of TLS-dependent services
• Monitor network traffic for unusual connection patterns to secure services
• Implement baseline monitoring for lsass.exe resource utilization

How to Mitigate CVE-2022-26915

Immediate Actions Required

• Apply the Microsoft security update for CVE-2022-26915 immediately on all affected systems
• Prioritize patching for internet-facing systems and critical infrastructure servers
• Review and restrict network access to services utilizing Schannel where possible
• Ensure SentinelOne agents are deployed and updated to detect exploitation attempts

Patch Information

Microsoft has released security updates to address this vulnerability as part of their April 2022 Patch Tuesday release. Administrators should consult the Microsoft Security Update Guide for CVE-2022-26915 for specific patch details and download links applicable to their environment.

Patches are available for all supported Windows versions, including extended security update (ESU) eligible systems like Windows Server 2008 and Windows 7.

Workarounds

• Implement network-level filtering to restrict access to TLS-enabled services from untrusted sources
• Consider deploying a Web Application Firewall (WAF) or reverse proxy to filter malicious requests before reaching vulnerable systems
• Segment networks to limit exposure of critical systems running unpatched Windows versions
• Monitor systems closely for signs of exploitation while awaiting patch deployment

# Verify Schannel-related patches are installed
wmic qfe list | findstr /i "KB5012591 KB5012596 KB5012604"

# Check current Schannel logging level (run in elevated PowerShell)
Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL" -Name EventLogging

# Enable enhanced Schannel logging for monitoring (requires restart)
# Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL" -Name EventLogging -Value 7