CVE-2024-6844
📋 TL;DR
This vulnerability in flask-cors 4.0.1 causes inconsistent CORS policy matching due to improper URL path normalization where '+' characters are converted to spaces. This can lead to either unauthorized cross-origin access or legitimate requests being blocked. Anyone using flask-cors 4.0.1 with CORS-configured endpoints containing '+' characters in their paths is affected.
💻 Affected Systems
- corydolphin/flask-cors
📦 What is this software?
Flask Cors by Flask Cors Project
⚠️ Risk & Real-World Impact
Worst Case
Attackers could bypass CORS restrictions and perform cross-origin attacks against endpoints that should be protected, potentially leading to data theft or CSRF attacks.
Likely Case
Inconsistent CORS behavior causing legitimate requests to be blocked or unauthorized cross-origin requests to succeed, leading to application errors or security policy violations.
If Mitigated
Limited impact if proper input validation and additional security layers are in place, though CORS policy enforcement remains unreliable.
🎯 Exploit Status
Exploitation requires knowledge of endpoint paths containing '+' characters and understanding of CORS policy bypass techniques.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.0.2
Vendor Advisory: https://github.com/corydolphin/flask-cors/security/advisories/GHSA-4j8q-2j8q-2j8q
Restart Required: Yes
Instructions:
1. Update flask-cors to version 4.0.2 or later using pip install flask-cors==4.0.2. 2. Restart your Flask application. 3. Verify the fix by testing endpoints with '+' characters in paths.
🔧 Temporary Workarounds
Avoid '+' in URL paths
allModify application endpoints to avoid using '+' characters in URL paths that have CORS configurations.
Use URL encoding
allEnsure all URL paths with special characters are properly URL-encoded before CORS processing.
🧯 If You Can't Patch
- Implement additional CORS validation at the application layer using middleware
- Use WAF rules to block suspicious cross-origin requests
🔍 How to Verify
Check if Vulnerable:
Check if using flask-cors 4.0.1 and if any CORS-configured endpoints contain '+' characters in their URL paths.Check Version:
pip show flask-cors | grep VersionVerify Fix Applied:
After updating to 4.0.2+, test endpoints with '+' characters to ensure CORS policies are correctly applied.📡 Detection & Monitoring
Log Indicators:
- CORS policy mismatches in application logs
- Unexpected cross-origin requests succeeding or being blocked
Network Indicators:
- HTTP requests with '+' characters in paths to CORS-protected endpoints
- Inconsistent CORS header responses
SIEM Query:
source="application.logs" AND ("CORS mismatch" OR "cross-origin" AND "+" AND "path")