CVE-2026-115927 Tornado: Event loop blocking and excess memory use from chunked bodies with many small chunks
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-115927?
CVE-2026-115927 is a medium-severity vulnerability in tornadoweb tornado, published on 26 Oct 2026.
Official description
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.
Which versions are affected by CVE-2026-115927?
2 open source packages ship an affected version, including tornado.
| Package | Affected | Fixed in |
|---|---|---|
tornado PyPI | All versions | 6.6 |
tornado PyPI | All versions | 6.6 |
How do I fix CVE-2026-115927?
Upgrade tornado to 6.6 or later.
Is CVE-2026-115927 being exploited?
There is no known exploitation of CVE-2026-115927 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-115927, ECHO-cb4d-5419-928b, GHSA-r4j5-9xpp-3985, MINI-f59q-3xqm-769h, UBUNTU-CVE-2026-115927.