CVE-2020-27847
📋 TL;DR
CVE-2020-27847 is a critical SAML signature validation bypass vulnerability in the dexidp/dex library. Attackers can forge SAML assertions to bypass authentication entirely, potentially gaining unauthorized access to systems relying on dex for identity management. This affects all organizations using dex versions before 2.27.0 for SAML authentication.
💻 Affected Systems
- github.com/dexidp/dex
📦 What is this software?
Dex by Linuxfoundation
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of all systems relying on dex for authentication, allowing attackers to impersonate any user, access sensitive data, and potentially pivot to other systems.
Likely Case
Unauthorized access to applications and services using dex for SAML authentication, leading to data breaches and privilege escalation.
If Mitigated
Limited impact if proper network segmentation, monitoring, and additional authentication layers are in place.
🎯 Exploit Status
Exploitation requires the attacker to have network access to the dex instance and knowledge of SAML message structure.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.27.0
Vendor Advisory: https://github.com/dexidp/dex/security/advisories/GHSA-m9hp-7r99-94h5
Restart Required: Yes
Instructions:
1. Stop dex service. 2. Update to dex version 2.27.0 or later. 3. Restart dex service. 4. Verify SAML authentication is working correctly.
🔧 Temporary Workarounds
Disable SAML Connector
allTemporarily disable SAML authentication if not essential
Modify dex configuration to remove or comment out SAML connector sections
Network Segmentation
allRestrict network access to dex instance
Configure firewall rules to limit access to dex ports from trusted networks only
🧯 If You Can't Patch
- Implement additional authentication layer (MFA) for all applications using dex
- Monitor dex logs for unusual authentication patterns and failed attempts
🔍 How to Verify
Check if Vulnerable:
Check dex version: if version < 2.27.0 and SAML connector is enabled, system is vulnerableCheck Version:
dex versionVerify Fix Applied:
Verify dex version is 2.27.0 or later and test SAML authentication flow📡 Detection & Monitoring
Log Indicators:
- Unexpected successful SAML authentications
- Authentication from unexpected sources
- Failed signature validation attempts
Network Indicators:
- Unusual SAML request patterns
- SAML assertions without proper signatures
SIEM Query:
source="dex" AND (event="authentication_success" OR event="saml_validation")🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=1907732
- https://github.com/dexidp/dex/security/advisories/GHSA-m9hp-7r99-94h5
- https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities/
- https://bugzilla.redhat.com/show_bug.cgi?id=1907732
- https://github.com/dexidp/dex/security/advisories/GHSA-m9hp-7r99-94h5
- https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities/
