# CVE-2025-67726

## Summary

- **CVE ID:** CVE-2025-67726
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** CWE-834, CWE-400
- **Published:** Dec 12, 2025
- **Last Modified:** Mar 13, 2026

## Description

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.

## Affected Products

- tornadoweb — tornado (< 6.5.3)

## References

- [CNA](https://github.com/tornadoweb/tornado/security/advisories/GHSA-jhmp-mqwm-3gq8)
- [CNA](https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd)
- [CNA](https://github.com/tornadoweb/tornado/releases/tag/v6.5.3)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.53%
- **EPSS Percentile:** 43.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._