CVE-2020-12676
📋 TL;DR
CVE-2020-12676 is a SAML authentication bypass vulnerability in FusionAuth's SAMLv2 library that allows attackers to forge authentication messages by sending SAML assertions without required digital signatures. This enables unauthorized access to applications using vulnerable versions of the library. Organizations using FusionAuth SAMLv2 0.2.3 for single sign-on are affected.
💻 Affected Systems
- FusionAuth SAMLv2 library
📦 What is this software?
Samlv2 by Fusionauth
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of SAML-protected applications, allowing attackers to impersonate any user and gain unauthorized access to sensitive systems and data.
Likely Case
Unauthorized access to applications using vulnerable SAML authentication, potentially leading to data breaches and privilege escalation.
If Mitigated
Limited impact with proper monitoring and compensating controls, but authentication bypass remains possible until patched.
🎯 Exploit Status
Attack tools like SAMLRaider can automate exploitation. The vulnerability is well-documented with public proof-of-concept details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.2.4 or later
Vendor Advisory: https://fusionauth.io/docs/v1/tech/release-notes/
Restart Required: Yes
Instructions:
1. Update FusionAuth SAMLv2 library to version 0.2.4 or later. 2. Update all applications using the library. 3. Restart affected services. 4. Test SAML authentication functionality.
🔧 Temporary Workarounds
SAML Signature Enforcement
allConfigure SAML service provider to require and validate digital signatures on all SAML assertions
Configure SAML service provider settings to require 'WantAssertionsSigned=true' and validate signatures
Network Segmentation
allRestrict access to SAML endpoints to trusted networks only
Implement firewall rules to limit SAML endpoint access to authorized IP ranges
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to detect and block SAML messages without signatures
- Enable enhanced logging and monitoring for SAML authentication attempts and review for suspicious patterns
🔍 How to Verify
Check if Vulnerable:
Check application dependencies for fusionauth-samlv2 version 0.2.3. For Java applications: check pom.xml or build.gradle for the vulnerable version.Check Version:
For Maven: mvn dependency:tree | grep fusionauth-samlv2. For Gradle: gradle dependencies | grep fusionauth-samlv2.Verify Fix Applied:
Verify fusionauth-samlv2 version is 0.2.4 or later. Test SAML authentication with invalid/missing signatures to ensure they are rejected.📡 Detection & Monitoring
Log Indicators:
- SAML authentication attempts without signatures
- Failed signature validation messages
- Unusual authentication patterns from unexpected sources
Network Indicators:
- SAML assertions transmitted without Signature elements
- SAML responses with manipulated XML structure
SIEM Query:
source="saml_auth.log" AND (message="signature validation failed" OR message="missing signature")🔗 References
- http://packetstormsecurity.com/files/159454/FusionAuth-SAMLv2-0.2.3-Message-Forging.html
- http://seclists.org/fulldisclosure/2020/Oct/1
- https://compass-security.com/fileadmin/Research/Advisories/2020-06_CSNC-2020-002_FusionAuth_Signature_Exclusion_Attack.txt
- https://github.com/SAMLRaider/SAMLRaider
- https://www.nds.ruhr-uni-bochum.de/media/nds/veroeffentlichungen/2012/08/22/BreakingSAML_3.pdf
- http://packetstormsecurity.com/files/159454/FusionAuth-SAMLv2-0.2.3-Message-Forging.html
- http://seclists.org/fulldisclosure/2020/Oct/1
- https://compass-security.com/fileadmin/Research/Advisories/2020-06_CSNC-2020-002_FusionAuth_Signature_Exclusion_Attack.txt
- https://github.com/SAMLRaider/SAMLRaider
- https://www.nds.ruhr-uni-bochum.de/media/nds/veroeffentlichungen/2012/08/22/BreakingSAML_3.pdf
