All vulnerabilities
CVE-2026-116577GHSA-pcg2-g6cj-q92c

Tornado: Quadratic CPU usage when parsing HTTP headers with line folding

tornadoweb tornado
Open in ThreatlineRecord JSON
CVSS
5.3Medium
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)No scoreNo FIRST EPSS score in this snapshot yet
Fixed inNone listedNo source names a fixed version. Check the vendor advisory below
Published26 Oct 2026Updated 26 Oct 2026CVE List

What fixes it

No source in this snapshot names a fixed version. The vendor advisories under References are the place to check.

Description

Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.

Text from CVE List

Affected versions 1

  • tornadoaffected: < 6.6CVE List

References 4