Advisory: Credential Disclosure in Web Interface of Crestron Device


When the administrative web interface of the Crestron HDMI switcher is
accessed unauthenticated, user credentials are disclosed which are valid
to authenticate to the web interface.

### Details

- Product: Crestron HD-MD4X2-4K-E
- Affected Versions: 1.0.0.2159
- Fixed Versions: -
- Vulnerability Type: Information Disclosure
- Security Risk: high
- Vendor URL: `https://de.crestron.com/Products/Video/HDMI-Solutions/HDMI-Switchers/HD-MD4X2-4K-E`
- Vendor Status: decided not to fix
- Advisory URL: `https://www.redteam-pentesting.de/advisories/rt-sa-2021-009`
- Advisory Status: published
- CVE: CVE-2022-23178
- CVE URL: `https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-23178`

### Introduction

"Crestron sets the gold standard for network security by leveraging the
most advanced technologies including 802.1x authentication, AES
encryption, Active Directory® credential management, JITC Certification,
SSH, secure CIP, PKI certificates, TLS, and HTTPS, among others, to
provide network security at the product level."

(from the vendor's homepage)

### More Details

Upon visiting the device's web interface using a web browser, a login
form is displayed requiring to enter username and password to
authenticate. The analysis of sent HTTP traffic revealed that in
addition to the loading of the website, a few more HTTP requests are
automatically triggered. One of the associated responses contains a
username and a password which can be used to authenticate as the
affected user.

### Proof of Concept

Requesting the URL "`http://crestron.example.com/`" via a web browser
results in multiple HTTP requests being sent. Among others, the
following URL is requested:

``` 
http://crestron.example.com/aj.html?a=devi&_=[...]
```

This request results in a response similar to the following:

``` 
HTTP/1.0 200 OK
Cache-Control: no-cache
Content-type: text/html

{
  "login_ur": 0,
  "front_val": [
    0,
    1
  ],
  "uname": "admin",
  "upassword": "password"
}
```

The values for the keys "uname" and "upassword" could be used to
successfully authenticate to the web interface as the affected user.

### Workaround

Reachability over the network can be restricted for access to the web
interface, for example by using a firewall.

### Fix

No fix known.

### Security Risk

As user credentials are disclosed to visitors of the web interface they
can directly be used to authenticate to it. The access allows to modify
the device's input and output settings as well as to upload and install
new firmware. Due to ease of exploitation and gain of administrative
access this vulnerability poses a high risk.

### Timeline

- 2021-10-06 Vulnerability identified
- 2021-11-15 Customer approved disclosure to vendor
- 2021-12-08 Vendor notified
- 2021-12-15 Vendor notified again
- 2021-12-21 Vendor response received: "The device in question doesn't support  
  Crestron's security practices. We recommend the HD-MD-4KZ alternative."
- 2021-12-22 Requested confirmation, that the vulnerability will not be addressed.
- 2021-12-28 Vendor confirms that the vulnerability will not be corrected.
- 2022-01-12 Advisory released

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