CVE-2026-59249

Description

Inconsistent interpretation of HTTP requests (HTTP response smuggling) vulnerability in elixir-mint mint allows a malicious HTTP/1 server to desynchronize a strict intermediary and the Mint client on the same pooled connection, enabling response-queue poisoning against subsequent requests that share the connection. The Mint.HTTP1.decode_body/5 function in lib/mint/http1.ex parses the chunk-size line of a Transfer-Encoding: chunked response with Integer.parse(data, 16). RFC 7230 defines chunk-size = 1*HEXDIG and forbids any sign prefix, but Integer.parse/2 accepts an optional leading + or -. A chunk-size line of +5 is accepted as a five-byte chunk; lines of +0 and -0 are accepted as the terminating zero-length chunk and end the message body early. An RFC-strict intermediary in the response path rejects these forms, so the intermediary and the Mint client disagree on where one response ends and the next begins. On a pooled keep-alive connection, an attacker-influenced origin can inject bytes that the client attributes to the next legitimate response on the same connection, poisoning the response queue and corrupting the responses returned to unrelated in-flight requests. This issue affects mint: from 0.1.0 before 1.9.3.

Severity (CVSS)

Weaknesses

• CWE-444 — CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Affected products

References

• https://github.com/elixir-mint/mint/security/advisories/GHSA-x3x7-96vm-6h2w (vendor-advisory related)
• https://cna.erlef.org/cves/CVE-2026-59249.html (related)
• https://osv.dev/vulnerability/EEF-CVE-2026-59249 (related)
• https://github.com/elixir-mint/mint/commit/fc7d16538db7e40b56ed489f08683225cb0197fa (patch)