CVE-2025-67726

Aliases:GHSA-jhmp-mqwm-3gq8PYSEC-2025-267
Advisory lineage Upstream: 0 Downstream: 40
Analyzed
Published: 12 Dec 2025, 06:13
Last modified:18 Dec 2025, 18:48

Vulnerability Summary

Overall Risk (default)
medium
30/100
CVSS Score
7.5 HIGH
v3.1 (cve.org)
EPSS Score
0.37% LOW
0% probability +0.25%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

12 Dec 2025, 06:13
Published
Vulnerability first disclosed
18 Dec 2025, 18:48
Last Modified
Vulnerability information updated

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.

CVSS Metrics

  • v3.1•HIGH•Score: 7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Trends

Current EPSS score: 0.37%• Percentile: 29%

Techniques & Countermeasures

  • CWE-400•Uncontrolled Resource Consumption

    The product does not properly control the allocation and maintenance of a limited resource.

  • CWE-834•Excessive Iteration

    The product performs an iteration or loop without sufficiently limiting the number of times that the loop is executed.

Affected Systems

  • PyPI•tornado

    < 6.5.3

  • tornadoweb•tornado

    < 6.5.3

References (6)