CVE-2026-55603 http-proxy-middleware is node.js http-proxy middleware
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 products and versions
| Product | Affected versions | Fixed in |
|---|---|---|
| http-proxy-middleware 4.0 | 4.0.0 → < 4.1.1 | 4.1.1 |
| http-proxy-middleware 3.0 | 3.0.4 → < 3.0.7 | 3.0.7 |