Mint HTTP/1 client applies chunked framing when chunked is not the final transfer coding, enabling response smuggling through intermediaries

Summary

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in elixir-mint mint allows a malicious HTTP/1 server to desynchronize an intermediary and the Mint client on a pooled connection, poisoning the responses to subsequent requests that share the connection. message_body/1 in lib/mint/http1.ex selects chunked framing when chunked is the first coding listed in a response's Transfer-Encoding fields. RFC 9112 section 6.3 applies chunked framing only when chunked is the final coding, and otherwise reads the body until the server closes the connection. For a response such as Transfer-Encoding: chunked, gzip, an intermediary that follows the RFC treats every byte up to the close as the body, while Mint ends the body at the zero-length chunk and parses the remaining bytes as the response to the next request on the connection. Mint also keeps the connection open after an HTTP/1.0 response, final or 1xx, that carries Transfer-Encoding and Connection: keep-alive. RFC 9112 section 6.1 requires treating the framing of such a message as faulty and closing the connection after it, so bytes after its chunked body are parsed as the response to the next request in the same way. This issue affects mint: from 0.1.0 before 1.10.2.

Timeline

1. Sep 28, 2026, 11:15 AM UTCCVE published
2. Sep 30, 2026, 1:16 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Sep 30, 2026, 1:17 PM UTCRecord last updated

Affected versions

• mint

  From 0.1.0 · fixed in 1.10.2

• elixir-mint/mint

  From 60089586ec7adc9fddb09f69a2f5919ba9ac7f33 · fixed in *

• mintHex

  From 0.1.0 · fixed in 1.10.2

References 6