# CVE-2026-55603: http-proxy-middleware: multipart/form-data field injection via unescaped CRLF in `fixRequestBody`

> Attackers can inject CRLF sequences to desynchronize multipart form data between proxy and backend, bypassing validation and modifying request fields.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Jun 2026
- **Updated:** 23 Jun 2026
- **Also known as:** ECHO-f223-e4bf-2265, GHSA-gcq2-9pq2-cxqm, MINI-4jjv-rwqw-g2j9, MINI-fh57-g8r4-chwc, MINI-fm5r-ph3h-g8qf, MINI-m846-mg27-9xxf, MINI-mp3p-7h88-j2r4, MINI-q8cr-26h2-9mvf, ROOT-APP-NPM-CVE-2026-55603

## What is CVE-2026-55603?

CVE-2026-55603 is a high-severity vulnerability in chimurai http-proxy-middleware, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### 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.

Weakness: CWE-93 (Improper Neutralization of CRLF Sequences)

## Which versions are affected by CVE-2026-55603?

4 open source packages ship an affected version, including http-proxy-middleware. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `http-proxy-middleware` | npm | From 3.0.4 | 3.0.7 |
| `http-proxy-middleware` | npm | From 3.0.4 | 3.0.7 |
| `http-proxy-middleware` | npm | From 4.0.0 | 4.1.1 |
| `http-proxy-middleware` | npm | From 4.0.0 | 4.1.1 |

Products: Chimurai Http-Proxy-Middleware.

## How do I fix CVE-2026-55603?

Upgrade http-proxy-middleware to a fixed version for your release line: 3.0.7 or 4.1.1.

## Is CVE-2026-55603 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55603 exists.

## Other vulnerabilities in chimurai http-proxy-middleware

- [CVE-2024-21536](https://insights.sbomify.com/CVE-2024-21536/): Denial of service in http-proxy-middleware (high 8.7)
- [CVE-2026-55602](https://insights.sbomify.com/CVE-2026-55602/): http-proxy-middleware `router` host+path substring matching allows Host-header-driven backend routing bypass (medium 6.9)
- [CVE-2025-32996](https://insights.sbomify.com/CVE-2025-32996/): http-proxy-middleware can call writeBody twice because "else if" is not used (medium 4.0)
- [CVE-2025-32997](https://insights.sbomify.com/CVE-2025-32997/): http-proxy-middleware allows fixRequestBody to proceed even if bodyParser has failed (medium 4.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55603 and fix it if it is affected.

What it is: CVE-2026-55603 is a high-severity vulnerability in chimurai http-proxy-middleware, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55603 exists.

Affected packages and fixed versions:
- http-proxy-middleware (npm): affected from 3.0.4; fixed in 3.0.7
- http-proxy-middleware (npm): affected from 3.0.4; fixed in 3.0.7
- http-proxy-middleware (npm): affected from 4.0.0; fixed in 4.1.1
- http-proxy-middleware (npm): affected from 4.0.0; fixed in 4.1.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55603/ (Markdown: https://insights.sbomify.com/CVE-2026-55603/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55603
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55603
- OSV: https://osv.dev/vulnerability/CVE-2026-55603

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55603/
Summaries are generated and may contain mistakes; the official description above is the record.