CVE-2026-94194: Mint HTTP/1 client applies chunked framing when chunked is not the final transfer coding, enabling response smuggling through intermediaries
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.
messagebody/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 1.11.0.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
elixir-mint/mintto a version that resolves this vulnerability.Fixed in 1.11.0
Event History
Frequently Asked Questions
Which connection patterns are exposed?
Exposure involves Mint HTTP/1 pooled connections where subsequent requests share a connection. A desynchronization can cause bytes from one response to be interpreted as the response to a later request on that same connection.
What must an attacker control to exploit this?
The attacker needs a malicious HTTP/1 server capable of sending malformed or ambiguously framed responses. Relevant cases include a Transfer-Encoding value such as "chunked, gzip", or an HTTP/1.0 final or 1xx response carrying both Transfer-Encoding and Connection: keep-alive.