# CVE-2026-55603: chimurai http-proxy-middleware CRLF injection in fixRequestBody

Source: https://junglewise.ai/threats/cve-2026-55603-chimurai-http-proxy-middleware-crlf-injection-in-fixrequestbody  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-22. Updated: 2026-06-22  
License: CC BY 4.0 with a link back

CVE-2026-55603 · Severity: high · CVSS 7.5 · Published 2026-06-22

A vulnerability in a popular Node.js web proxy tool allows attackers to bypass security filters and manipulate data sent to backend servers. By including special hidden characters in a web request, an attacker can trick the proxy into adding unauthorized fields, such as changing a user's role to 'admin' or altering prices. This can lead to unauthorized access or data tampering even if the proxy has security rules in place to prevent such actions.

Technologies: [http-proxy-middleware (npm)](https://junglewise.ai/threats/technologies/http-proxy-middleware). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-55603 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-55603 being exploited in the wild.

**How severe is CVE-2026-55603?** High severity, with a CVSS score of 7.5, published 22 June 2026.

**Which products and versions are affected?** http-proxy-middleware (npm) SEMVER:introduced=3.0.4,fixed=3.0.7.

**Is there a fix for CVE-2026-55603?** Yes. http-proxy-middleware (npm): upgrade to 3.0.7 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-55603 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-55603?** Check whether you run http-proxy-middleware (npm) 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.

## How to fix

- http-proxy-middleware (npm): upgrade to 3.0.7 or later

  ```sh
  npm install http-proxy-middleware@3.0.7
  ```


## Technical details

A CRLF injection vulnerability exists in the `fixRequestBody()` helper of http-proxy-middleware. When the outgoing request is set to `multipart/form-data`, the `handlerFormDataBodyData()` function performs direct string interpolation of `req.body` keys and values into the multipart wire format without neutralizing carriage return or line feed characters. An attacker can exploit this by providing a payload containing `\r\n` sequences to terminate the current form part and inject entirely new parts. This results in a parameter desynchronization where the proxy's security middleware validates one set of fields while the backend server receives and processes an altered set. The vulnerability is exploitable when the proxy uses a non-multipart parser (like JSON or URL-encoded) for input but forwards the request as multipart. This is fixed in versions 3.0.7 and 4.1.1.

## Affected products

- chimurai http-proxy-middleware >= 3.0.4, < 3.0.7; >= 4.0.0, < 4.1.1

## Identifiers

- CVE-2026-55603
- GHSA-gcq2-9pq2-cxqm

## Timeline

- 2026-06-17: advisory: GitHub Security Advisory published
- 2026-06-22: disclosed: CVE published to NVD

## References

- [https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-gcq2-9pq2-cxqm](https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-gcq2-9pq2-cxqm)

## Related threats

- [chimurai http-proxy-middleware routing bypass via Host header substring match](https://junglewise.ai/threats/cve-2026-55602-chimurai-http-proxy-middleware-routing-bypass-via-host-header)
- [http-proxy-middleware double write in fixRequestBody](https://junglewise.ai/threats/cve-2025-32996-http-proxy-middleware-double-write-in-fixrequestbody)
- [http-proxy-middleware fixRequestBody error handling bypass](https://junglewise.ai/threats/cve-2025-32997-http-proxy-middleware-fixrequestbody-error-handling-bypass)
- [http-proxy-middleware denial of service in path filtering](https://junglewise.ai/threats/cve-2024-21536-http-proxy-middleware-denial-of-service-in-path-filtering)