AIKIDO-2026-380869
tornado is vulnerable to Denial of Service (DoS)
75
High Risk
This Affects:
tornadoTL;DR
Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs without passing a max_num_fields bound. A body composed almost entirely of separators produces tens of millions of fields, and this parsing runs synchronously on the event loop before any handler executes. Because the server is single-threaded, one such request stalls the whole process and blocks every other connection. The fix limits form-encoded bodies to a bounded number of arguments by default.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and accept application/x-www-form-urlencoded request bodies (Tornado’s default for most handlers).
Background info
tornado is vulnerable to Denial of Service (DoS) in versions 0.0.1 - 6.5.7.
How to fix this
Upgrade the tornado library to the patch version.
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SOC 2Compliant
ISO 27001Compliant