CVE-2025-67726

Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters

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.

Scores

Faiblesses (CWE)

• CWE-834
• CWE-400

Avis

• GHSA-jhmp-mqwm-3gq8 — Tornado: Quadratic DoS via Crafted Multipart Parameters
• PYSEC-2025-267 — 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 he

Références européennes

• ENISA EUVD · EUVD-2025-203029
• GCVE · GCVE-0-2025-67726

Avis du CERT-FR

• CERTFR-2026-AVI-1056 — Multiples vulnérabilités dans les produits Splunk · cert.ssi.gouv.fr
• CERTFR-2026-AVI-0901 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
• CERTFR-2026-AVI-0641 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr

Configurations affectées (CPE NVD)

• cpe:2.3:a:tornadoweb:tornado:*:*:*:*:*:*:*:* < 6.5.3

Produits affectés

Références

• https://github.com/tornadoweb/tornado/security/advisories/GHSA-jhmp-mqwm-3gq8
• https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd
• https://github.com/tornadoweb/tornado/releases/tag/v6.5.3

Sources