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

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). 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
    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

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