CVE-2026-115927
Tornado: Event loop blocking and excess memory use from chunked bodies with many small chunks
Impact
Tornado is a Python web framework and asynchronous networking library. Prior to 6.6.0, Tornado decodes HTTP/1.1 chunked transfer encoding by processing body data that has already arrived without yielding to the event loop. A remote unauthenticated peer can send millions of one-byte chunks to monopolize the process event loop and stall every other connection served by that process, while lowering max_body_size only limits the duration of each request. For handlers that do not use @stream_request_body, retaining each chunk as a separate object can consume roughly twenty times the received body size, and SimpleAsyncHTTPClient has the same event-loop behavior when reading a response from a malicious server. This issue is fixed in version 6.6.0.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | tornado | < 6.6 | 6.6 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-r4j5-9xpp-3985
- https://github.com/tornadoweb/tornado/security/advisories/GHSA-r4j5-9xpp-3985
- https://nvd.nist.gov/vuln/detail/CVE-2026-115927
- https://github.com/tornadoweb/tornado/pull/3773
- https://github.com/tornadoweb/tornado/commit/ceab33581489751a66fba8566ad6d5960d4b01c8
- https://github.com/tornadoweb/tornado/releases/tag/v6.6.0