CVE-2026-59249 Other in mint
A malicious server can desynchronize the Mint HTTP client and intermediaries via chunk-size parsing, poisoning response queues on pooled connections.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-59249?
CVE-2026-59249 is a medium-severity vulnerability in elixir-mint mint, published on 16 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-444
Which versions are affected by CVE-2026-59249?
1 open source package ship an affected version, including mint.
| Package | Affected | Fixed in |
|---|---|---|
mint Hex | From 0.1.0 | 1.9.3 |
How do I fix CVE-2026-59249?
Upgrade mint to 1.9.3 or later.
Is CVE-2026-59249 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59249 exists.
Sources
Also known as EEF-CVE-2026-59249, GHSA-x3x7-96vm-6h2w.