Resource exhaustion in Tornadoweb Tornado
CVE-2026-115927
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.
Vulnerability class: DoS (Denial of Service)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Tornadoweb Tornado — versions < 6.6.0
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-115927?
- CVE-2026-115927 is a medium-severity vulnerability in Tornadoweb Tornado, classified under Uncontrolled Resource Consumption. CVSS score: 5.3/10. Published 2026-10-26.
- How severe is CVE-2026-115927?
- Medium severity. CVSS v3 base score is 5.3 out of 10.