# CVE-2026-49753: Elixir Mint HTTP response smuggling via lenient Content-Length parsing

Source: https://junglewise.ai/threats/cve-2026-49753-elixir-mint-http-response-smuggling-via-lenient-content-length  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-02. Updated: 2026-07-10  
License: CC BY 4.0 with a link back

CVE-2026-49753 · Severity: medium · CVSS 6.3 · Published 2026-06-02

Mint, a popular HTTP client for the Elixir programming language, contains a flaw in how it handles web server responses. It incorrectly accepts certain non-standard characters in the 'Content-Length' header, which can lead to 'response smuggling.' This could allow a malicious server or intermediary to interfere with web traffic, potentially causing data from one user's request to leak into another user's session.

Technologies: [Elixir-Mint Mint](https://junglewise.ai/threats/technologies/mint). Vendors: [Elixir-Mint](https://junglewise.ai/threats/vendors/elixir-mint).

## Quick answers

**Is CVE-2026-49753 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-49753 being exploited in the wild.

**How severe is CVE-2026-49753?** Medium severity, with a CVSS score of 6.3, published 2 June 2026.

**Which products and versions are affected?** Elixir-Mint Mint < 1.9.0, >= 0.1.0, < 1.9.0.

**Is there a fix for CVE-2026-49753?** A patch was published on 1.9.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-49753 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-49753?** Check whether you run Elixir-Mint Mint at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in 'Elixir.Mint.HTTP1.Parse':content_length_header/1 due to the use of Integer.parse/1, which permits an optional '+' sign prefix forbidden by RFC 7230. This creates a parser differential when Mint is deployed behind strict fronting proxies or load balancers that either reject or reframe such headers. An attacker (typically a compromised or malicious upstream server) can exploit this desynchronization to perform response smuggling. When connections are pooled or shared across trust boundaries, this can result in cross-request data leaks or response stream corruption. The issue is fixed in version 1.9.0.

## Affected products

- elixir-mint mint < 1.9.0

## Identifiers

- CVE-2026-49753
- GHSA-mjqx-c6f6-7rc2

## Timeline

- 2026-06-02: disclosed
- 2026-07-09: advisory: GitHub Advisory published
- 1.9.0: patched

## References

- [https://api.github.com/users/PJUllrich](https://api.github.com/users/PJUllrich)
- [https://github.com/PJUllrich](https://github.com/PJUllrich)
- [https://api.github.com/users/PJUllrich/gists%7B/gist_id%7D](https://api.github.com/users/PJUllrich/gists%7B/gist_id%7D)
- [https://api.github.com/users/PJUllrich/repos](https://api.github.com/users/PJUllrich/repos)
- [https://avatars.githubusercontent.com/u/10426523?v=4](https://avatars.githubusercontent.com/u/10426523?v=4)
- [https://api.github.com/users/PJUllrich/events%7B/privacy%7D](https://api.github.com/users/PJUllrich/events%7B/privacy%7D)

## Related threats

- [Mint HTTP request/response smuggling in transfer encoding parsing](https://junglewise.ai/threats/cve-2026-94194-inconsistent-interpretation-of-http-requests-http-request)
- [Elixir Mint HTTP/2 frame buffer exhaustion](https://junglewise.ai/threats/cve-2026-92103-allocation-of-resources-without-limits-or-throttling)
- [Mint HTTP/2 header list memory exhaustion denial of service](https://junglewise.ai/threats/cve-2026-91043-allocation-of-resources-without-limits-or-throttling)
- [Elixir Mint HTTP request smuggling in chunked transfer encoding](https://junglewise.ai/threats/cve-2026-82672-inconsistent-interpretation-of-http-requests-http-request)
- [elixir-mint HTTP/1 parser algorithmic complexity denial of service](https://junglewise.ai/threats/cve-2026-82729-elixir-mint-http-1-parser-algorithmic-complexity-denial-of)