CVE-2026-49855: Tornadoweb Tornado

High severity, CVSS 7.5. EPSS: 0.6% chance of exploitation in the next 30 days.

Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.

Affected products

• Tornadoweb Tornado: before 6.5.6 (fixed in 6.5.6)

Published 2026-07-14. Last modified 2026-07-16.