PyPI · tornado
Tornado: Quadratic DoS via Repeated Header Coalescing
The HTTPHeaders.add method in Tornado accumulates values using string concatenation when the same header name is repeated. Due to Python string immutability, each concatenation copies the entire string, resulting in O(n²) time complexity.
Given Tornado's single event loop architecture, a single maliciously crafted HTTP request can block the server's event loop for an extended period, causing a Denial of Service (DoS).
Severity: High if max_header_size has been increased from its default, low if it has its default value of 64KB.
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Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.