CVE-2026-49756 Multipart form-data header injection in Req via unescaped name/filename/content_type
Attackers can inject CRLF sequences into multipart form data via Req, allowing header injection and part smuggling in outgoing requests.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-49756?
CVE-2026-49756 is a low-severity vulnerability in wojtekmach req, published on 8 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in wojtekmach Req allows multipart parameter smuggling via attacker-influenced part metadata.
Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part headers by interpolating the caller-supplied name, filename, and content_type values directly into the content-disposition and content-type lines with no escaping or CRLF stripping. A value containing ", \r, or \n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and prepends a smuggled part of the attacker's choosing.
This is reachable through every supported way of supplying a part. It is particularly easy when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. Any application that forwards user-controlled filenames (or field names / MIME types) through Req.post/2 with form_multipart: lets an attacker inject arbitrary headers into the outgoing multipart body or smuggle additional fields and parts into the request the victim service sends downstream.
This issue affects req: from 0.5.3 before 0.6.0.
Weakness: CWE-93
Which versions are affected by CVE-2026-49756?
3 open source packages ship an affected version, including req. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
req Hex | From 0.5.3 | 0.6.0 |
req Hex | From 0.5.3 | 0.6.0 |
req Hex | From 0.5.3 | 0.6.0 |
Products include Wojtekmach Req.
How do I fix CVE-2026-49756?
Upgrade req to 0.6.0 or later.
Is CVE-2026-49756 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49756 exists.
Other vulnerabilities in wojtekmach req
Sources
Also known as EEF-CVE-2026-49756, GHSA-px9f-whj3-246m.