{"cve":"CVE-2025-67726","nvd":{"published":"2025-12-12T07:15:44.920","modified":"2026-10-07T20:10:01.970","status":"Analyzed","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_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-400","CWE-834"],"references":["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"],"products":["tornadoweb:tornado"],"source":"nvd","synced_at":"2026-10-19T22:16:40.427100871+00:00"},"epss":{"cve":"CVE-2025-67726","score":0.00535,"percentile":0.44889,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-jhmp-mqwm-3gq8","url":"https://osv.dev/vulnerability/GHSA-jhmp-mqwm-3gq8","summary":"Tornado: Quadratic DoS via Crafted Multipart Parameters","modified":"2026-07-20T19:15:27.583657512Z","packages":[{"ecosystem":"PyPI","name":"tornado","purl":"pkg:pypi/tornado","ranges":["<6.5.3"],"fixed":["6.5.3"]}]},{"id":"PYSEC-2025-267","url":"https://osv.dev/vulnerability/PYSEC-2025-267","summary":"","modified":"2026-07-13T07:15:45.375541292Z","packages":[{"ecosystem":"PyPI","name":"tornado","purl":"pkg:pypi/tornado","ranges":["<6.5.3"],"fixed":["6.5.3"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}