Tornado before 6.4.1 ignores duplicate Transfer-Encoding: chunked headers, treating requests as having no message body and parsing the chunked body as a subsequent request. Attackers can exploit this inconsistency when Tornado is deployed behind proxies to perform HTTP request smuggling, enabling access control bypass, cache poisoning, or connection desynchronization.
https://github.com/tornadoweb/tornado/security/advisories/GHSA-753j-mpmx-qq6g
Published: 2026-09-15
Updated: 2026-09-16
Base Score: 6.1
Vector: CVSS2#AV:N/AC:H/Au:N/C:P/I:C/A:N
Severity: Medium
Base Score: 7.5
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N
Severity: High
Base Score: 9
Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:H/VA:N/SC:L/SI:H/SA:N
Severity: Critical
EPSS: 0.00351