CVE-2021-45890
📋 TL;DR
CVE-2021-45890 is an authentication bypass vulnerability in AuthGuard's BasicAuthProvider that allows authentication using inactive user identifiers. This affects all systems running AuthGuard versions before 0.9.0 that use basic authentication. Attackers can gain unauthorized access to protected resources by using deactivated or disabled accounts.
💻 Affected Systems
- AuthGuard
📦 What is this software?
Authguard by Authguard Project
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise where attackers gain administrative access using deactivated privileged accounts, leading to data theft, system manipulation, or lateral movement.
Likely Case
Unauthorized access to protected resources and sensitive data using inactive user accounts, potentially leading to privilege escalation.
If Mitigated
Limited impact with proper monitoring and access controls, but still represents an authentication bypass that should be addressed.
🎯 Exploit Status
Exploitation requires knowledge of inactive user identifiers and their credentials. The vulnerability is in the authentication logic itself.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.9.0
Vendor Advisory: https://github.com/AuthGuard/AuthGuard/commit/9783b1143da6576028de23e15a1f198b1f937b82
Restart Required: Yes
Instructions:
1. Update AuthGuard to version 0.9.0 or later. 2. Restart the AuthGuard service. 3. Verify the fix by testing authentication with inactive accounts.
🔧 Temporary Workarounds
Switch to alternative authentication provider
allTemporarily disable BasicAuthProvider and use a different authentication method until patching is possible.
# Edit AuthGuard configuration to use alternative auth provider
# Restart AuthGuard service
🧯 If You Can't Patch
- Implement additional authentication layer (2FA/MFA) for all users
- Monitor authentication logs for attempts using inactive accounts and implement alerting
🔍 How to Verify
Check if Vulnerable:
Test authentication with a known inactive user account. If authentication succeeds, the system is vulnerable.Check Version:
Check AuthGuard version in configuration files or via application logsVerify Fix Applied:
After patching, attempt authentication with an inactive user account. Authentication should fail.📡 Detection & Monitoring
Log Indicators:
- Authentication attempts using inactive or disabled user accounts
- Successful logins from accounts marked as inactive
Network Indicators:
- Basic authentication requests to AuthGuard endpoints
- Unusual authentication patterns
SIEM Query:
source="authguard" AND (event="authentication_success" AND user_status="inactive")🔗 References
- https://github.com/AuthGuard/AuthGuard/commit/9783b1143da6576028de23e15a1f198b1f937b82
- https://github.com/AuthGuard/AuthGuard/compare/v0.8.0...v0.9.0
- https://github.com/AuthGuard/AuthGuard/issues/166
- https://github.com/AuthGuard/AuthGuard/pull/181
- https://github.com/AuthGuard/AuthGuard/commit/9783b1143da6576028de23e15a1f198b1f937b82
- https://github.com/AuthGuard/AuthGuard/compare/v0.8.0...v0.9.0
- https://github.com/AuthGuard/AuthGuard/issues/166
- https://github.com/AuthGuard/AuthGuard/pull/181
