CVE-2026-116577: DoS (CVSS 5.3)

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.

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CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS — Exploit Prediction

0.0038

Probability of exploitation

0.32%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-407 CWE-407

CWE-770 CWE-770

References

Other References

https://github.com/tornadoweb/tornado/commit/1b7a1dc9f340f52de929852e8125aa12f25297c9 https://github.com/tornadoweb/tornado/pull/3765 https://github.com/tornadoweb/tornado/releases/tag/v6.6.0 https://github.com/tornadoweb/tornado/security/advisories/GHSA-pcg2-g6cj-q92c

Frequently Asked Questions

What is CVE-2026-116577? +

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. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-116577? +

CVE-2026-116577 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0038, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-116577? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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