# CVE-2026-115927: Tornado HTTP/1.1 chunked encoding denial of service

Source: https://junglewise.ai/threats/cve-2026-115927-tornado-is-a-python-web-framework-and-asynchronous-networking  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-26. Updated: 2026-10-26  
License: CC BY 4.0 with a link back

CVE-2026-115927 · Severity: medium · CVSS 5.3 · Published 2026-10-26

Tornado is a Python web framework used to build web applications and APIs. A remote attacker can send specially crafted HTTP requests with many tiny chunks to exhaust the server's event loop, preventing it from handling other client requests and causing a denial of service. The vulnerability affects all Tornado versions before 6.6.0.

Technologies: [tornado (PyPI)](https://junglewise.ai/threats/technologies/tornado), [Tornado Project Tornado](https://junglewise.ai/threats/technologies/tornado-project-tornado). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi), [Tornado Project](https://junglewise.ai/threats/vendors/tornado-project).

## Quick answers

**Is CVE-2026-115927 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-115927 being exploited in the wild.

**How severe is CVE-2026-115927?** Medium severity, with a CVSS score of 5.3, published 26 October 2026.

**Which products and versions are affected?** tornado (PyPI) < 6.6, ECOSYSTEM:introduced=0,fixed=6.6; Tornado Project Tornado before 6.6.0.

**Is there a fix for CVE-2026-115927?** Yes. tornado (PyPI): upgrade to 6.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-115927 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-115927?** Check whether you run tornado (PyPI) or Tornado Project Tornado at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- tornado (PyPI): upgrade to 6.6 or later

  ```sh
  pip install "tornado>=6.6"
  ```


## Technical details

Tornado's HTTP/1.1 chunked transfer encoding decoder processes body data without yielding to the event loop, allowing an unauthenticated remote attacker to send millions of one-byte chunks to monopolize CPU. Additionally, handlers lacking @stream_request_body retain each chunk as a separate object, consuming roughly 20x the received body size in memory. The vulnerability stems from insufficient event loop yields during chunk processing and chunk buffering inefficiency; it is fixed in version 6.6.0 by yielding every 256KB and coalescing small chunks.

## Affected products

- Tornado Project Tornado before 6.6.0

## Identifiers

- CVE-2026-115927
- GHSA-r4j5-9xpp-3985

## Timeline

- 2026-10-26: disclosed
- 2026-10-07: patched

## References

- [https://github.com/tornadoweb/tornado/commit/ceab33581489751a66fba8566ad6d5960d4b01c8](https://github.com/tornadoweb/tornado/commit/ceab33581489751a66fba8566ad6d5960d4b01c8)
- [https://github.com/tornadoweb/tornado/pull/3773](https://github.com/tornadoweb/tornado/pull/3773)

## Related threats

- [Tornado open redirect in RedirectHandler URL templates](https://junglewise.ai/threats/cve-2026-116578-tornado-is-a-python-web-framework-and-asynchronous-networking)
- [Tornado HTTP header parser quadratic CPU consumption via line folding](https://junglewise.ai/threats/cve-2026-116577-tornado-is-a-python-web-framework-and-asynchronous-networking)
- [Tornado StaticFileHandler path traversal via symlinks](https://junglewise.ai/threats/cve-2026-103263-tornado-staticfilehandler-follows-symlinks-outside-static-root)
- [Tornado CurlAsyncHTTPClient unbounded memory accumulation in decompression](https://junglewise.ai/threats/cve-2026-103262-tornado-curlasynchttpclient-enforces-no-response-size-limit)
- [Tornado unbounded query string field parsing DoS](https://junglewise.ai/threats/cve-2026-103261-tornado-unbounded-query-string-argument-count-allows-event-loop)