CVE-2026-49753 HTTP response smuggling in Mint HTTP/1 client via lenient Content-Length parsing
An attacker-controlled server can desynchronize HTTP response framing in the Mint Elixir client, potentially leaking data across shared 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-2026-49753?
CVE-2026-49753 is a medium-severity vulnerability in elixir-mint mint, published on 2 Jun 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 Request/Response Smuggling') vulnerability in elixir-mint Mint allows attacker-controlled HTTP/1 servers to desynchronise response framing on shared connections.
Mint's HTTP/1 Content-Length parser, Mint.HTTP1.Parse.content_length_header/1 in lib/mint/http1/parse.ex, parses the header value with Integer.parse/1, which accepts an optional + or - sign prefix. The length >= 0 guard rejects negatives, but inputs such as +0 or +123 are returned as valid lengths. RFC 7230 specifies Content-Length = 1*DIGIT, with no sign character permitted.
A fronting proxy or load balancer that strictly enforces the grammar will reject or reframe a header like Content-Length: +0, while Mint silently treats it as zero. When Mint reuses the socket (keep-alive, pipelining, or any pooled connection shared across requesters), the parser disagreement is a response-smuggling primitive: the proxy delimits the body one way, Mint another, and bytes from one response get attributed to the next. Where the same Mint connection is shared across trust boundaries, an attacker-controlled upstream can leak bytes into a different consumer's response stream.
This issue affects mint: from 0.1.0 before 1.9.0.
Weakness: CWE-444
Which versions are affected by CVE-2026-49753?
3 open source packages ship an affected version, including mint.
| Package | Affected | Fixed in |
|---|---|---|
mint Hex | All versions | 1.9.0 |
mint Hex | All versions | 1.9.0 |
mint Hex | From 0.1.0 | 1.9.0 |
How do I fix CVE-2026-49753?
Upgrade mint to 1.9.0 or later.
Is CVE-2026-49753 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49753 exists.
Sources
Also known as EEF-CVE-2026-49753, GHSA-mjqx-c6f6-7rc2.