Vulnerability in Chimurai Http-Proxy-Middleware
CVE-2026-55603
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.
Vulnerability class: CRLF Injection
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N.
EPSS exploit prediction
EPSS: 0.003 (18.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 19th percentile — 18.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000
Affected products
- Chimurai Http-Proxy-Middleware — versions >= 3.0.4, < 3.0.7, >= 4.0.0, < 4.1.1
Weakness classification (CWE)
References
- github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-gcq2-9pq2-cx… (Exploit, Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-55603?
- CVE-2026-55603 is a high-severity vulnerability in Chimurai Http-Proxy-Middleware, classified under CRLF Injection. CVSS score: 7.5/10. Published 2026-06-22.
- How severe is CVE-2026-55603?
- High severity. CVSS v3 base score is 7.5 out of 10.