Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop

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 0.0035, the 28th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

1. 31 Oct 2026, 14:10 UTC First seen by agentprime
2. 31 Oct 2026, 14:10 UTC Confirmed by OSV

Sources

• GitHub Advisory Database: GHSA-mpf4-983q-p7j4
• OSV: GHSA-mpf4-983q-p7j4
• github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4
• nvd.nist.gov/vuln/detail/CVE-2026-82397
• github.com/tornadoweb/tornado/pull/3704
• github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de
• github.com/tornadoweb/tornado
• github.com/tornadoweb/tornado/releases/tag/v6.5.8

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.