High (7.5) in tornadoweb tornado. EPSS 1.0% chance of exploitation in the next 30 days. Fixed in tornado 6.4.2.
Tornado is a Python web framework and asynchronous networking library. The algorithm used for parsing HTTP cookies in Tornado versions prior to 6.4.2 sometimes has quadratic complexity, leading to excessive CPU consumption when parsing maliciously-crafted cookie headers. This parsing occurs in the event loop thread and may block the processing of other requests. Version 6.4.2 fixes the issue.
Severity
CVSS 3.1
7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
1.0% chance of exploitation in the next 30 days; higher than 64% of CVEs (scores of 2026-10-31)