EEF-CVE-2026-114216

Chunk extensions accept bare LF and CR, enabling request smuggling in Bandit

## Summary Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in the HTTP/1.1 chunked body reader of mtrudel bandit allows an unauthenticated remote attacker to smuggle a second request past a front-end proxy via a chunk extension that contains a bare LF. The chunked reader in `lib/bandit/http1/socket.ex` takes the chunk-size line to be everything up to the first CRLF and discards everything after `;` without checking it against the RFC 9112 `chunk-ext` grammar, so bare LF, bare CR and other control bytes pass. A proxy that ends the size line at a bare LF reads `2;\nxx\r\n40\r\n...` as one request whose second chunk holds a `GET /admin`, while Bandit ends the body early and dispatches `GET /admin` as a separate pipelined request. Deployments without such a proxy in front of Bandit are not affected. This issue affects bandit: from 1.12.4 before 1.14.0. ## Details **1. Unchecked extension.** In `lib/bandit/http1/socket.ex`, the chunked body reader takes the chunk-size line to be everything up to the first CRLF. Anything after `;` is thrown away without being checked against the RFC 9112 §7.1.1 `chunk-ext` grammar, so bare LF, bare CR and other control bytes are accepted. The 16-byte size-line cap does not help, because the payload needs only 5 bytes. **2. Bandit's reading.** For the body `2;\nxx\r\n40\r\n0\r\n\r\nGET /admin ...`, Bandit takes `2;\nxx` as the size line and `40` as the 2-byte chunk, and the embedded `0\r\n\r\n` ends the body. Bandit then runs `GET /admin` as a second pipelined request. **3. The proxy's reading.** A proxy that ends the size line at the bare LF sees only one POST, with the chunk `xx` and a 0x40-byte chunk that holds the `GET /admin` bytes. ## Proof of concept 1. Run Bandit with a Plug that reads the body and records each request's method and path. 2. On one connection, send `POST /public` with `Transfer-Encoding: chunked` and the body `2;\nxx\r\n40\r\n0\r\n\r\n`, followed directly by `GET /admin HTTP/1.1` with `Content-Length: 7` and the body `\r\n0\r\n\r\n`. 3. Bandit dispatches both `POST /public` with the body `40` and `GET /admin`. A proxy that ends lines at a bare LF would have forwarded the same bytes as the single `POST /public`. ## Impact Behind a front-end proxy that treats a bare LF as a line ending and forwards chunked bodies unchanged, an unauthenticated attacker can have Bandit run requests the proxy never saw, getting past the proxy's access controls. ## Workarounds Where the front-end proxy can reach Bandit over HTTP/2, disable HTTP/1 with `http_1_options: [enabled: false]`, so that the chunked body reader never runs.