CVE-2026-91991

Tornado before 6.5.7 contains a credential leak vulnerability in CurlAsyncHTTPClient where pycurl handles are reused across requests without proper state clearing. Attackers can obtain sensitive credentials by issuing requests through the same client instance, allowing TLS certificates or proxy authentication to persist across unintended requests.

Tornado before 6.5.8 contains a memory amplification vulnerability in parse_multipart_form_data that splits multipart data before validating the max_parts limit. Attackers can send crafted multipart requests with many parts to create large transient lists, exhausting server memory and causing denial of service.

Tornado before 6.4.1 contains a CRLF injection vulnerability in CurlAsyncHTTPClient that fails to reject carriage return and line feed characters in request headers. Attackers can inject CRLF sequences into header values to inject arbitrary headers or construct entirely new HTTP requests.

Tornado before 6.4.1 ignores duplicate Transfer-Encoding: chunked headers, treating requests as having no message body and parsing the chunked body as a subsequent request. Attackers can exploit this inconsistency when Tornado is deployed behind proxies to perform HTTP request smuggling.

Tornado before 6.3.3 contains an HTTP request smuggling vulnerability due to improper parsing of Content-Length headers accepting non-standard characters. Attackers can send crafted HTTP requests with these characters to bypass proxy validation and smuggle requests when deployed behind certain proxies.

Tornado before version 6.5.8 does not limit the number of fields when parsing application/x-www-form-urlencoded request bodies. An unauthenticated request with millions of fields can stall the single-threaded event loop and delay every connection.

A vulnerability in Tornado before version 6.5.6 allows unlimited decompression of gzip data, potentially leading to memory exhaustion by a malicious server or SimpleAsyncHTTPClient.

In Tornado before version 6.5.6, the optional native extension tornado.speedups implemented websocket_mask without validating that the mask argument is exactly four bytes. This allows the C function to read up to three bytes beyond the provided buffer when reached through Tornado XSRF token decoding with the native extension active.

In Tornado before version 6.5.6, SimpleAsyncHTTPClient shallow-copied redirected requests and removed only the Host header, leaving Authorization, auth_username, auth_password, and auth_mode in place when a redirect changed scheme, host, or port. This issue is fixed in version 6.5.6.

In Tornado before 6.5.5, cookie attribute injection could occur because the domain, path, and samesite arguments to .RequestHandler.set_cookie were not checked for crafted characters.