CVE-2023-41890
📋 TL;DR
The Sustainsys.Saml2 library has an authentication bypass vulnerability where SAML responses aren't properly validated. Attackers can impersonate legitimate identity providers or manipulate stored authentication state, potentially allowing unauthorized access. Applications using this library for SAML-based authentication are affected.
💻 Affected Systems
- Sustainsys.Saml2 library for ASP.NET
📦 What is this software?
Saml2 by Sustainsys
Saml2 by Sustainsys
⚠️ Risk & Real-World Impact
Worst Case
Complete authentication bypass allowing attackers to impersonate any user, potentially gaining administrative privileges and full system access.
Likely Case
Unauthorized access to user accounts, privilege escalation, or session hijacking through manipulated SAML responses.
If Mitigated
Limited impact with proper validation in place, potentially only affecting specific authentication flows.
🎯 Exploit Status
Exploitation requires understanding of SAML protocol and ability to craft malicious responses, but no public exploit code is known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.0.3 or 2.9.2
Vendor Advisory: https://github.com/Sustainsys/Saml2/security/advisories/GHSA-fv2h-753j-9g39
Restart Required: Yes
Instructions:
1. Update NuGet package to version 1.0.3 or 2.9.2. 2. Update package reference in project file. 3. Rebuild and redeploy application. 4. Restart application services.
🔧 Temporary Workarounds
Custom validation using AcsCommandResultCreated
allImplement custom issuer validation in the AcsCommandResultCreated notification handler
Implement custom validation logic in AcsCommandResultCreated event handler
🧯 If You Can't Patch
- Implement additional validation layers in authentication logic
- Monitor authentication logs for unusual issuer patterns or authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check package version in project file or NuGet packages.config for versions below 1.0.3 or 2.9.2Check Version:
Check project's packages.config or .csproj file for Sustainsys.Saml2 versionVerify Fix Applied:
Verify package version is 1.0.3 or higher (for v1) or 2.9.2 or higher (for v2)📡 Detection & Monitoring
Log Indicators:
- Multiple authentication attempts with different issuer values
- Authentication from unexpected identity providers
- Failed issuer validation attempts
Network Indicators:
- Unusual SAML response patterns
- SAML responses from unexpected sources
SIEM Query:
Search for authentication events with mismatched issuer values or from unexpected identity providers🔗 References
- https://github.com/Sustainsys/Saml2/issues/712
- https://github.com/Sustainsys/Saml2/issues/713
- https://github.com/Sustainsys/Saml2/security/advisories/GHSA-fv2h-753j-9g39
- https://github.com/Sustainsys/Saml2/issues/712
- https://github.com/Sustainsys/Saml2/issues/713
- https://github.com/Sustainsys/Saml2/security/advisories/GHSA-fv2h-753j-9g39
