CVE-2020-36255
📋 TL;DR
CVE-2020-36255 is a vulnerability in IdentityModel's Branca token implementation that allows attackers to modify and forge authentication tokens. This affects applications using ScottBrady.IdentityModel for authentication before version 1.3.0. Attackers could bypass authentication or impersonate users.
💻 Affected Systems
- ScottBrady.IdentityModel (IdentityModel)
📦 What is this software?
Identitymodel by Identitymodel Project
⚠️ Risk & Real-World Impact
Worst Case
Complete authentication bypass allowing attackers to impersonate any user, access sensitive data, or perform unauthorized administrative actions.
Likely Case
Authentication token forgery leading to unauthorized access to user accounts and potential privilege escalation.
If Mitigated
Limited impact with proper token validation and additional authentication layers in place.
🎯 Exploit Status
Exploitation requires understanding of Branca token format but is straightforward once understood.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.3.0
Vendor Advisory: https://github.com/scottbrady91/IdentityModel/compare/1.2.0...1.3.0
Restart Required: Yes
Instructions:
1. Update IdentityModel package to version 1.3.0 or later. 2. Restart the application. 3. Regenerate all existing Branca tokens.
🔧 Temporary Workarounds
Disable Branca tokens
allTemporarily disable Branca token authentication until patching is complete
Implement additional token validation
allAdd custom validation logic to verify token integrity beyond the vulnerable implementation
🧯 If You Can't Patch
- Implement network segmentation to isolate affected systems
- Deploy Web Application Firewall (WAF) with token validation rules
🔍 How to Verify
Check if Vulnerable:
Check if IdentityModel package version is below 1.3.0 in your project dependenciesCheck Version:
Check package manager (NuGet) for IdentityModel versionVerify Fix Applied:
Verify IdentityModel package version is 1.3.0 or higher and test token validation functionality📡 Detection & Monitoring
Log Indicators:
- Unexpected authentication failures
- Multiple failed token validation attempts
- Authentication from unusual locations
Network Indicators:
- Unusual authentication patterns
- Token reuse from different IPs
SIEM Query:
Authentication logs where token validation fails or succeeds unexpectedly🔗 References
- https://github.com/scottbrady91/IdentityModel/compare/1.2.0...1.3.0
- https://github.com/scottbrady91/IdentityModel/issues/3
- https://github.com/scottbrady91/IdentityModel/issues/4
- https://github.com/scottbrady91/IdentityModel/compare/1.2.0...1.3.0
- https://github.com/scottbrady91/IdentityModel/issues/3
- https://github.com/scottbrady91/IdentityModel/issues/4
