CVE-2021-29455
📋 TL;DR
This vulnerability in Grassroot Platform allows attackers to forge valid JSON Web Tokens by exploiting improper signature verification during JWT refresh operations. This affects all Grassroot Platform deployments before version 1.3.1, potentially enabling unauthorized access to user accounts and administrative functions.
💻 Affected Systems
- Grassroot Platform
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete account takeover, administrative privilege escalation, unauthorized access to sensitive community organizing data, and potential manipulation of grassroots mobilization efforts.
Likely Case
Unauthorized access to user accounts, session hijacking, and potential data exposure of community organizing information.
If Mitigated
Limited impact with proper network segmentation and additional authentication layers, but still represents an authentication bypass vulnerability.
🎯 Exploit Status
Exploitation requires understanding of JWT refresh mechanisms but is technically straightforward once identified.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.3.1
Vendor Advisory: https://github.com/grassrootza/grassroot-platform/security/advisories/GHSA-f65w-6xw8-6734
Restart Required: Yes
Instructions:
1. Update Grassroot Platform to version 1.3.1 or later. 2. Restart the application server. 3. Verify the JWT refresh endpoint is disabled or properly secured.
🔧 Temporary Workarounds
Disable JWT Refresh Endpoint
allDisable or block access to the JWT refresh functionality entirely
# Configure application to disable /api/auth/refresh endpoint
# Use web server configuration to block /api/auth/refresh
Implement Additional Authentication Checks
allAdd secondary authentication mechanisms for sensitive operations
# Implement multi-factor authentication
# Add IP-based restrictions for authentication endpoints
🧯 If You Can't Patch
- Implement network segmentation to isolate Grassroot Platform from sensitive systems
- Deploy a Web Application Firewall (WAF) with JWT validation rules
🔍 How to Verify
Check if Vulnerable:
Check if running Grassroot Platform version earlier than 1.3.1 and if JWT refresh endpoint (/api/auth/refresh) is accessible without proper signature verification.Check Version:
Check application configuration files or use: grep -r 'version' /path/to/grassroot/config/Verify Fix Applied:
Verify version is 1.3.1 or later and test that JWT refresh endpoint either returns error or requires proper signature validation.📡 Detection & Monitoring
Log Indicators:
- Multiple failed JWT refresh attempts
- Unusual JWT refresh patterns
- Authentication from unexpected locations
Network Indicators:
- Unusual traffic to /api/auth/refresh endpoint
- JWT refresh requests with modified signatures
SIEM Query:
source="grassroot" AND (uri_path="/api/auth/refresh" AND status=200) | stats count by src_ip🔗 References
- https://github.com/grassrootza/grassroot-platform/
- https://github.com/grassrootza/grassroot-platform/commit/a2e6e885f8183a066d938cf909fd813a7af7d67f
- https://github.com/grassrootza/grassroot-platform/security/advisories/GHSA-f65w-6xw8-6734
- https://github.com/grassrootza/grassroot-platform/
- https://github.com/grassrootza/grassroot-platform/commit/a2e6e885f8183a066d938cf909fd813a7af7d67f
- https://github.com/grassrootza/grassroot-platform/security/advisories/GHSA-f65w-6xw8-6734
