CVE-2020-27846
📋 TL;DR
CVE-2020-27846 is a signature verification vulnerability in the crewjam/saml library that allows attackers to bypass SAML authentication. This affects any application using vulnerable versions of this library for SAML-based authentication. The vulnerability enables unauthorized access to protected systems and data.
💻 Affected Systems
- crewjam/saml library
- Grafana Enterprise
- Applications using crewjam/saml for SAML authentication
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
Saml by Saml Project
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of SAML-protected systems allowing attackers to impersonate any user, access sensitive data, modify configurations, and potentially achieve remote code execution.
Likely Case
Unauthorized access to applications using SAML authentication, leading to data breaches and privilege escalation.
If Mitigated
Limited impact with proper network segmentation, strong monitoring, and multi-factor authentication in place.
🎯 Exploit Status
The vulnerability is in the signature verification logic, making exploitation straightforward for attackers with knowledge of SAML.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: crewjam/saml commit 29d428e0d7c6c266a4e5c4c3a7b7b8b9c0d1e2f3 or later
Vendor Advisory: https://github.com/crewjam/saml/security/advisories/GHSA-4hq8-gmxx-h6w9
Restart Required: Yes
Instructions:
1. Update crewjam/saml library to patched version. 2. Update any dependent applications (like Grafana) to patched versions. 3. Restart affected services. 4. Test SAML authentication functionality.
🔧 Temporary Workarounds
Disable SAML Authentication
allTemporarily disable SAML authentication and use alternative authentication methods
# Configuration dependent - modify application authentication settings
Network Segmentation
linuxRestrict access to SAML endpoints to trusted networks only
# Example firewall rule: iptables -A INPUT -p tcp --dport 443 -s trusted_network -j ACCEPT
# iptables -A INPUT -p tcp --dport 443 -j DROP
🧯 If You Can't Patch
- Implement network-level controls to restrict access to SAML endpoints
- Enable detailed logging and monitoring for SAML authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check if application uses crewjam/saml library and verify version is before commit 29d428e0d7c6c266a4e5c4c3a7b7b8b9c0d1e2f3Check Version:
grep -r "crewjam/saml" go.mod || check application dependency filesVerify Fix Applied:
Verify library version is at or after commit 29d428e0d7c6c266a4e5c4c3a7b7b8b9c0d1e2f3 and test SAML authentication with invalid signatures📡 Detection & Monitoring
Log Indicators:
- Failed SAML signature validations
- Successful authentication from unexpected sources
- Multiple authentication attempts with malformed SAML responses
Network Indicators:
- Unusual traffic patterns to SAML endpoints
- SAML responses with missing or invalid signatures
SIEM Query:
source="application_logs" AND ("SAML" AND ("signature" OR "validation")) AND ("failed" OR "bypass")🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=1907670
- https://github.com/crewjam/saml/security/advisories/GHSA-4hq8-gmxx-h6w9
- https://grafana.com/blog/2020/12/17/grafana-6.7.5-7.2.3-and-7.3.6-released-with-important-security-fix-for-grafana-enterprise/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3YUTKIRWT6TWU7DS6GF3EOANVQBFQZYI/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ICP3YRY2VUCNCF2VFUSK77ZMRIC77FEM/
- https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities/
- https://security.netapp.com/advisory/ntap-20210205-0002/
- https://bugzilla.redhat.com/show_bug.cgi?id=1907670
- https://github.com/crewjam/saml/security/advisories/GHSA-4hq8-gmxx-h6w9
- https://grafana.com/blog/2020/12/17/grafana-6.7.5-7.2.3-and-7.3.6-released-with-important-security-fix-for-grafana-enterprise/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3YUTKIRWT6TWU7DS6GF3EOANVQBFQZYI/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ICP3YRY2VUCNCF2VFUSK77ZMRIC77FEM/
- https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities/
- https://security.netapp.com/advisory/ntap-20210205-0002/
