tornadoweb Tornado up to 6.5.7 Request Body Parsing tornado/web.py RequestHandler._execute infinite loop

Summaryinfo

A vulnerability identified as problematic has been detected in tornadoweb Tornado up to 6.5.7. Affected by this issue is the function RequestHandler._execute of the file tornado/web.py of the component Request Body Parsing. Performing a manipulation results in infinite loop. This vulnerability is reported as CVE-2026-82397. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as problematic, was found in tornadoweb Tornado up to 6.5.7. This affects the function RequestHandler._execute of the file tornado/web.py of the component Request Body Parsing. The manipulation with an unknown input leads to a infinite loop vulnerability. CWE is classifying the issue as CWE-835. The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. This is going to have an impact on availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-82397 since 08/29/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 6.5.8 eliminates this vulnerability.

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Productinfo

Vendor

• tornadoweb

Name

• Tornado

Version

• 6.5.0
• 6.5.1
• 6.5.2
• 6.5.3
• 6.5.4
• 6.5.5
• 6.5.6
• 6.5.7

Website

• Product: https://github.com/tornadoweb/tornado/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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