CVE-2026-82397: tornadoweb tornado Uncontrolled Resource Consumption

Vulnerability summary

CVE-2026-82397 is a high (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in tornadoweb tornado. EPSS estimates a 0.35% chance of exploitation in the next 30 days, higher than 26.6% of scored vulnerabilities.

Timeline

1. 31-08-2026
   PublishedVulnerability first disclosed.
2. 02-09-2026
   Last modifiedVulnerability information updated.

Description

Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.
• CWE-1284Improper Validation of Specified Quantity in InputThe product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.