Affected: sanic-org sanic

Sanic is an opensource python web server/framework. In version 25.12.0, Sanic's core HTTP/1.1 chunked-body handling does not fully consume the trailer-part after the terminating zero chunk before reusing the keep-alive connection buffer. A remote unauthenticated client can place attacker-controlled bytes in that trailer region, causing Sanic to parse and route them as a hidden second request after the outer request. This breaks HTTP request-boundary integrity and can provide a request-smuggling primitive when Sanic is deployed behind intermediaries. This issue is fixed in version 25.12.1.

Affected: PyPI: sanic

## Description

Sanic's HTTP/1.1 chunked-body handling does not fully consume the `trailer-part` after the terminating `0\r\n` chunk. Because of that, attacker-controlled bytes left in the connection buffer after the first chunked request can be interpreted as the start of a new HTTP request on the same keep-alive connection. In the attached verified proof, a single outer `POST /` request that correctly returns `405 Method Not Allowed` is followed, within the same TCP send, by a hidden second request smuggled through the chunked trailer area. Sanic parses and executes that second request as a real independent request.

The issue is a request-boundary integrity failure in Sanic's core HTTP/1.1 parser. The verified impact is not speculative. The attached proof shows that one TCP payload produces two server responses: first the expected `405` for the outer `POST /`, then a separate `200 OK` for a hidden `GET /`. A second exploit variant changes the hidden request path and receives a real `404 Not Found`, proving that the hidden second request is not a hard-coded artifact but an actually routed backend request. A control case with a two-character trailer field name shifts the leftover bytes from `GET` to `:GET`, which changes the second response accordingly and confirms that the root cause is incorrect trailer consumption rather than legitimate pipelining.

## Steps To Reproduce

1. Start a Sanic HTTP/1.1 service on a keep-alive connection path. In the verified run, the local ta…