CVE-2025-62706
📋 TL;DR
CVE-2025-62706 is a denial-of-service vulnerability in Authlib's JWE implementation where DEFLATE decompression lacks size limits. Attackers can send specially crafted tokens that cause excessive memory and CPU consumption when decrypted, potentially crashing affected services. This affects any system using Authlib versions before 1.6.5 for JWE token processing.
💻 Affected Systems
- Authlib
📦 What is this software?
Authlib by Authlib
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to memory exhaustion and CPU saturation, potentially affecting multiple services in shared environments.
Likely Case
Service degradation or temporary outages for affected endpoints, requiring restarts and causing user disruption.
If Mitigated
Minimal impact with proper input validation and rate limiting; failed token processing with error logging.
🎯 Exploit Status
Requires ability to supply decryptable tokens to the target system. Attack complexity is moderate as it requires understanding of JWE token structure and compression.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.6.5
Vendor Advisory: https://github.com/authlib/authlib/security/advisories/GHSA-g7f3-828f-7h7m
Restart Required: No
Instructions:
1. Update Authlib to version 1.6.5 or later using pip: 'pip install --upgrade authlib>=1.6.5'. 2. Verify the update completed successfully. 3. No restart required as this is a library update.
🔧 Temporary Workarounds
Reject zip=DEF tokens
allConfigure application to reject or strip zip=DEF parameter from inbound JWEs at the application boundary.
Implement bounded decompression
allFork and modify Authlib to add size limits to DEFLATE decompression using decompressobj().decompress(data, MAX_SIZE).
Enforce token size limits
allImplement strict maximum token sizes and fail fast on oversized inputs, combined with rate limiting.
🧯 If You Can't Patch
- Implement WAF rules to block or limit JWE tokens with zip=DEF parameter
- Deploy rate limiting and input validation at the application perimeter
🔍 How to Verify
Check if Vulnerable:
Check Authlib version: 'python -c "import authlib; print(authlib.__version__)"' and verify it's below 1.6.5.Check Version:
python -c "import authlib; print(authlib.__version__)"Verify Fix Applied:
Verify version is 1.6.5 or higher using the same command, and test JWE token processing with zip=DEF to ensure proper error handling.📡 Detection & Monitoring
Log Indicators:
- High memory usage spikes
- Process crashes or restarts
- Error logs related to JWE decompression failures
- Unusually large token processing times
Network Indicators:
- High volume of JWE tokens to authentication endpoints
- Repeated token submission patterns
SIEM Query:
source=application_logs AND ("JWE" OR "zip=DEF") AND ("memory" OR "crash" OR "timeout")