Vulnerability Description
Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, a single maliciously crafted HTTP request can block the server's event loop for an extended period, caused by the HTTPHeaders.add method. The function accumulates values using string concatenation when the same header name is repeated, causing a Denial of Service (DoS). Due to Python string immutability, each concatenation copies the entire string, resulting in O(n²) time complexity. The severity can vary from high if max_header_size has been increased from its default, to low if it has its default value of 64KB. This issue is fixed in version 6.5.3.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Tornadoweb | Tornado | < 6.5.3 |
Related Weaknesses (CWE)
References
- https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6Patch
- https://github.com/tornadoweb/tornado/releases/tag/v6.5.3Release Notes
- https://github.com/tornadoweb/tornado/security/advisories/GHSA-c98p-7wgm-6p64Vendor Advisory
FAQ
What is CVE-2025-67725?
CVE-2025-67725 is a vulnerability with a CVSS score of 7.5 (HIGH). Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, a single maliciously crafted HTTP request can block the server's event loop for an extended period, ...
How severe is CVE-2025-67725?
CVE-2025-67725 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2025-67725?
Check the references section above for vendor advisories and patch information. Affected products include: Tornadoweb Tornado.