CVE-2025-67726: Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

• tornadoweb tornadobefore 6.5.3

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

• tornadoweb tornado

  • < 6.5.3affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Other highest-scoring records for the same primary product.

• CVE-2024-14029Tornado before 6.4.1 HTTP Request Smuggling via Transfer-Encoding
  36Monitor
• CVE-2023-54397Tornado before 6.3.3 HTTP Request Smuggling via Content-Length
  36Monitor
• CVE-2026-103262Tornado before 6.5.9 Denial of Service via CurlAsyncHTTPClient
  34Monitor

Published before and after this one in the same product

• ← EarlierCVE-2025-67724Dec 12, 2025 · Tornado vulnerable to Header Injection and XSS via reason argument
  24Monitor
• ← EarlierCVE-2025-67725Dec 12, 2025 · Tornado is Vulnerable to Quadratic DoS via Repeated Header Coalescing
  30Monitor
• Later →CVE-2026-31958Mar 11, 2026 · Tornado has a DoS due to too many multipart parts
  34Monitor

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

1function expand(node) {2  return node.children.map(expand);3}

1const MAX_DEPTH = 32;2function expand(node, depth = 0) {3  if (depth > MAX_DEPTH) throw new Error("too deep");4  return node.children.map((c) => expand(c, depth + 1));5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.