CVE-2026-116577 Tornado: Quadratic CPU usage when parsing HTTP headers with line folding
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-116577?
CVE-2026-116577 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, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.
Which versions are affected by CVE-2026-116577?
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-2026-116577?
Upgrade tornado to 6.6 or later.
Is CVE-2026-116577 being exploited?
There is no known exploitation of CVE-2026-116577 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-116577, ECHO-02a2-2a6c-6e79, GHSA-pcg2-g6cj-q92c, MINI-4rr5-62fx-gqmp, UBUNTU-CVE-2026-116577.