CVE-2026-55603: Chimurai HTTP-Proxy-Middleware

High severity, CVSS 7.5. EPSS: 0.3% chance of exploitation in the next 30 days.

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

• Chimurai HTTP-Proxy-Middleware: from 3.0.4, before 3.0.7 (fixed in 3.0.7); from 4.0.0, before 4.1.1 (fixed in 4.1.1)

Published 2026-06-22. Last modified 2026-06-24.