Vulnerability · Published Jun 22, 2026 · Assigned by GitHub_M
CVE-2026-55603http-proxy-middleware: multipart/form-data field injection via unescaped CRLF in `fixRequestBody`
High 7.5
In plain English
A high-severity security flaw in http-proxy-middleware from chimurai. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 21% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
http-proxy-middleware is node.js http-proxy middleware. From 3.0.4 until 3.0.7 and 4.1.1, fixRequestBody() is the library's documented helper for re-emitting a request body that was already consumed by a body parser. When the outgoing Content-Type is multipart/form-data, it rebuilds the body with handlerFormDataBodyData(), which interpolates each req.body key and value directly into the multipart wire format without neutralizing CR/LF. A \r\n inside a value (or key) lets an attacker close the current part and inject an entirely new form part. Because the proxy's own body parser saw a single opaque value, any gateway-side policy or validation performed on req.body is evaluated against a different set of fields than the upstream backend ultimately parses a request/parameter desynchronization across the trust boundary. This vulnerability is fixed in 3.0.7 and 4.1.1.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | http-proxy-middleware | 3.0.7 | GHSA-gcq2-9pq2-cxqm |
| npm | http-proxy-middleware | 4.1.1 | GHSA-gcq2-9pq2-cxqm |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| chimurai | http-proxy-middleware | >= 3.0.4, < 3.0.7>= 4.0.0, < 4.1.1 |
Weakness: CWE-93 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N