# 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.

- **Severity:** Low 2.1 (`CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Jun 2026
- **Updated:** 8 Jun 2026
- **Also known as:** EEF-CVE-2026-49756, GHSA-px9f-whj3-246m

## 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 (Improper Neutralization of CRLF Sequences)

## Which versions are affected by CVE-2026-49756?

3 open source packages ship an affected version, including req. It affects 1 product.


| Package | Ecosystem | 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: 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

- [CVE-2026-49755](https://insights.sbomify.com/CVE-2026-49755/): Decompression bomb DoS in Req via auto-decoded archive and compressed response bodies (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49756 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49756 exists.

Affected packages and fixed versions:
- req (Hex): affected from 0.5.3; fixed in 0.6.0
- req (Hex): affected from 0.5.3; fixed in 0.6.0
- req (Hex): affected from 0.5.3; fixed in 0.6.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-49756/ (Markdown: https://insights.sbomify.com/CVE-2026-49756/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49756
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49756
- OSV: https://osv.dev/vulnerability/CVE-2026-49756

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49756/
Summaries are generated and may contain mistakes; the official description above is the record.