CVE-2025-67726

Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.py is used to parse specific HTTP header values, such as those in multipart/form-data and repeatedly calls string.count() within a nested loop while processing quoted semicolons. If an attacker sends a request with a large number of maliciously crafted parameters in a Content-Disposition header, the server's CPU usage increases quadratically (O(n²)) during parsing. Due to Tornado's single event loop architecture, a single malicious request can cause the entire server to become unresponsive for an extended period. This issue is fixed in version 6.5.3.

The following products are affected by CVE-2025-67726 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2025-67726.

URL	Resource
https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd
https://github.com/tornadoweb/tornado/releases/tag/v6.5.3
https://github.com/tornadoweb/tornado/security/advisories/GHSA-jhmp-mqwm-3gq8
https://nvd.nist.gov/vuln/detail/CVE-2025-67726
https://www.cve.org/CVERecord?id=CVE-2025-67726