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

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

• CISA KEV Not listed.
• EPSS 0.0038, the 32nd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

1. 26 Oct 2026, 20:20 UTC Confirmed by the CVE List
2. 31 Oct 2026, 14:07 UTC First seen by agentprime
3. 31 Oct 2026, 14:07 UTC Confirmed by OSV

Sources

• GitHub Advisory Database: GHSA-pcg2-g6cj-q92c
• OSV: GHSA-pcg2-g6cj-q92c
• github.com/tornadoweb/tornado/security/advisories/GHSA-pcg2-g6cj-q92c
• nvd.nist.gov/vuln/detail/CVE-2026-116577
• github.com/tornadoweb/tornado/pull/3765
• github.com/tornadoweb/tornado/commit/1b7a1dc9f340f52de929852e8125aa12f25297c9
• github.com/tornadoweb/tornado
• github.com/tornadoweb/tornado/releases/tag/v6.6.0

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.