Is CVE-2026-116577 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-116577 being exploited in the wild.

How severe is CVE-2026-116577?

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 before 6.6.

Is there a fix for CVE-2026-116577?

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-2026-116577 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-116577?

Check whether you run tornado (PyPI) or 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.

CVE-2026-116577: Tornado HTTP header parser quadratic CPU consumption via line folding

Q: Which products and versions are affected?

tornado (PyPI) < 6.6, ECOSYSTEM:introduced=0,fixed=6.6; Tornado before 6.6.

Q: Is there a fix for CVE-2026-116577?

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.

Q: How is CVE-2026-116577 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-116577?

Check whether you run tornado (PyPI) or 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.

CVE-2026-116577 · Severity: medium · CVSS 5.3 · Published 2026-10-26

Tornado is a popular Python web framework used to build high-performance web applications. An attacker can send specially crafted HTTP requests with obsolete line-folding continuations to trigger excessive CPU usage on the server's processing thread, preventing the application from serving legitimate requests. This denial-of-service attack requires no authentication and can significantly impact application availability.

Technologies: tornado (PyPI), Tornado. Vendors: PyPI, Tornado.

Quick answers

Is CVE-2026-116577 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-116577 being exploited in the wild.
How severe is CVE-2026-116577?: 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 before 6.6.
Is there a fix for CVE-2026-116577?: 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-2026-116577 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-116577?: Check whether you run tornado (PyPI) or 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
```
pip install "tornado>=6.6"
```

Technical details

Tornado's HTTP header parser prior to version 6.6 accepts obsolete HTTP line folding syntax and repeatedly concatenates continuation lines, causing quadratic CPU consumption. An unauthenticated client can submit a malicious header block before application code executes, blocking the IOLoop thread and other connections. The attack cost scales with the configured max_header_size parameter.

Affected products

Tornado Tornado before 6.6

Identifiers

CVE-2026-116577
GHSA-pcg2-g6cj-q92c

Timeline

2026-10-26: disclosed
2026-10-06: patched

References

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