Medium 5.3Published Oct 26, 2026

CVE-2026-116577Tornado: Quadratic CPU usage when parsing HTTP headers with line folding

Updated under an hour ago (Oct 29, 2026, 2:00 AM ET)

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No exploitation reported and no EPSS estimate yet.

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Every CVE for tornadoweb tornado

Exploited in the last 30 days

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.

CVSS: 5.3 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness (CWE): CWE-407, CWE-770
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Oct 26, 2026
First seen by InfoSec Signals: Oct 26, 2026

Affected products

Affected products

tornadoweb tornado tornadoweb:tornado (from the name)	before 6.6	CNA record

References

References

https://github.com/tornadoweb/tornado/security/advisories/GHSA-pcg2-g6cj-q92c	x-refsource-confirm
https://github.com/tornadoweb/tornado/pull/3765	x-refsource-misc
https://github.com/tornadoweb/tornado/commit/1b7a1dc9f340f52de929852e8125aa12f25297c9	x-refsource-misc
https://github.com/tornadoweb/tornado/releases/tag/v6.6.0	x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.