# CVE-2026-55602: http-proxy-middleware `router` host+path substring matching allows Host-header-driven backend routing bypass

> Attackers can bypass backend routing restrictions by crafting Host headers that exploit unanchored substring matching in http-proxy-middleware configurations.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA: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:** CLEANSTART-2026-FK52853, CLSA-2026-1784509824, CLSA-2026-1788806507, CLSA-2026-1788806602, CLSA-2026-1788806634, CLSA-2026-1788867095, ECHO-3f08-2076-9e96, GHSA-64mm-vxmg-q3vj, MINI-2284-g2vg-vq2j, MINI-4g8g-c69f-5jvf, MINI-54gc-hrhh-jh37, MINI-55f6-57rh-96f5, MINI-6p2v-85xh-8xx2, MINI-7xrc-v9w2-3vh9, MINI-jfcc-gp28-hp3j, MINI-jmw9-rjhr-9xpc, MINI-m93q-wv9h-3r59, MINI-qm93-cxhf-v75v, MINI-xjrr-fh47-cgr9, ROOT-APP-NPM-CVE-2026-55602

## What is CVE-2026-55602?

CVE-2026-55602 is a medium-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 0.16.0 until 2.0.10, 3.0.6, and 4.1.0, http-proxy-middleware documents router proxy-table entries as host, path, or host+path selectors, but the host+path implementation uses unanchored substring matching on attacker-controlled request metadata. As a result, a crafted Host header that is only a superstring match for a configured host+path key can still route a request to an unintended backend. This vulnerability is fixed in 2.0.10, 3.0.6, and 4.1.0.

Weakness: CWE-20 (Improper Input Validation), CWE-187 (Partial String Comparison)

## Which versions are affected by CVE-2026-55602?

6 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 0.16.0 | 2.0.10 |
| `http-proxy-middleware` | npm | From 0.16.0 | 2.0.10 |
| `http-proxy-middleware` | npm | From 3.0.0 | 3.0.6 |
| `http-proxy-middleware` | npm | From 3.0.0 | 3.0.6 |
| `http-proxy-middleware` | npm | From 4.0.0 | 4.1.0 |
| `http-proxy-middleware` | npm | From 4.0.0 | 4.1.0 |

Products: Chimurai Http-Proxy-Middleware.

## How do I fix CVE-2026-55602?

Upgrade http-proxy-middleware to a fixed version for your release line: 2.0.10, 3.0.6 or 4.1.0.

## Is CVE-2026-55602 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55602 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-2026-55603](https://insights.sbomify.com/CVE-2026-55603/): http-proxy-middleware: multipart/form-data field injection via unescaped CRLF in `fixRequestBody` (high 7.5)
- [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-2026-55602 and fix it if it is affected.

What it is: CVE-2026-55602 is a medium-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-2026-55602 exists.

Affected packages and fixed versions:
- http-proxy-middleware (npm): affected from 0.16.0; fixed in 2.0.10
- http-proxy-middleware (npm): affected from 0.16.0; fixed in 2.0.10
- http-proxy-middleware (npm): affected from 3.0.0; fixed in 3.0.6
- http-proxy-middleware (npm): affected from 3.0.0; fixed in 3.0.6
- http-proxy-middleware (npm): affected from 4.0.0; fixed in 4.1.0
- http-proxy-middleware (npm): affected from 4.0.0; fixed in 4.1.0

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-2026-55602/ (Markdown: https://insights.sbomify.com/CVE-2026-55602/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55602
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55602
- OSV: https://osv.dev/vulnerability/CVE-2026-55602

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55602/
Summaries are generated and may contain mistakes; the official description above is the record.