Vulnerability in http-proxy-middleware (CVE-2026-55603)
Summary
Vulnerability in http-proxy-middleware (CVE-2026-55603). Data can be tampered with by attackers. Exploitable via req.body. Mitigation: upgrade to 4.1.1 or later.
Original description
The description as published by the source.
Summary
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:
// dist/handlers/fix-request-body.js
function handlerFormDataBodyData(contentType, data) {
const boundary = contentType.replace(/^.*boundary=(.*)$/, '$1');
let str = '';
for (const [key, value] of Object.entries(data)) {
str += `--${boundary}\r\nContent-Disposition: form-data; name="${key}"\r\n\r\n${value}\r\n`;
}
}
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.
By contrast, the sibling output branches are safe: application/json uses JSON.stringify (escapes control chars) and application/x-www-form-urlencoded uses querystring.stringify (percent-encodes). Only the multipart branch lacks escaping.
Preconditions
All three must hold; this narrows real-world exposure and is the basis for AC:H:
- The proxy app populates `req.bo…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-55603 has been found in http-proxy-middleware.
Attackers can target a specific entry point like req.body over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 7.5/10.
What to do: upgrade http-proxy-middleware to 4.1.1 or later.
If unsure, ask your IT team or search "http-proxy-middleware CVE-2026-55603" on the vendor's site.
CVE-2026-55603 (http-proxy-middleware) — CWE-93 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: req.body / JSON.stringify / querystring.stringify / express.urlencoded
Patched: 4.1.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-93) exists in http-proxy-middleware. Attackers reach the vulnerable code path via req.body without authentication.
Check the vendor advisory for the affected versions of http-proxy-middleware. Attack surface: req.body / JSON.stringify / querystring.stringify / express.urlencoded.
Severity: High (CVSS 7.5/10). Data can be tampered with by attackers.
Update to 4.1.1.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'http-proxy-middleware' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'http-proxy-middleware' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
http-proxy-middlewareを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade http-proxy-middleware to 4.1.1ステージング環境で 4.1.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- package github.com
- web github.com
- web github.com