ABB Cylon FLXeon 9.3.5 (uukl.js) Predictable Salt and Weak Hashing Algorithm

Title: ABB Cylon FLXeon 9.3.5 (uukl.js) Predictable Salt and Weak Hashing Algorithm Advisory ID: ZSL-2025-5936 Type: Local/Remote Impact:…

ABB Cylon FLXeon 9.3.5 (uukl.js) Predictable Salt and Weak Hashing Algorithm

Vendor: ABB Ltd.

Product web page: https://www.global.abb

Affected version: FLXeon Series (FBXi Series, FBTi Series, FBVi Series)

CBX Series (FLX Series)

CBT Series

CBV Series

Firmware: <=9.3.5

Summary: BACnet® Smart Building Controllers. ABB’s BACnet portfolio features a

series of BACnet® IP and BACnet MS/TP field controllers for ASPECT® and INTEGRA™

building management solutions. ABB BACnet controllers are designed for intelligent

control of HVAC equipment such as central plant, boilers, chillers, cooling towers,

heat pump systems, air handling units (constant volume, variable air volume, and

multi-zone), rooftop units, electrical systems such as lighting control, variable

frequency drives and metering.

The FLXeon Controller Series uses BACnet/IP standards to deliver unprecedented

connectivity and open integration for your building automation systems. It’s scalable,

and modular, allowing you to control a diverse range of HVAC functions.

Desc: The ABB Cylon FLXeon BACnet controller’s /api/uukl.js module implements password

verification and update mechanisms using the insecure MD5 hash function alongside weak

salt generation via Math.random(). This constitutes a cryptographic vulnerability where

password hashes are susceptible to collision and brute-force attacks due to MD5’s known

weaknesses and the low entropy of the salt. Specifically, in the verify() and change()

functions, passwords are hashed using MD5 with predictable, non-cryptographically secure

salts, then stored in plaintext-accessible files. This undermines the integrity of the

authentication process, enabling attackers with file system access or knowledge of the

implementation to precompute hash values or mount dictionary attacks.

Tested on: Linux Kernel 5.4.27

Linux Kernel 4.15.13

NodeJS/8.4.0

Express

Vulnerability discovered by Gjoko ‘LiquidWorm’ Krstic

@zeroscience

Advisory ID: ZSL-2025-5936

Advisory URL: https://www.zeroscience.mk/en/vulnerabilities/ZSL-2025-5936.php

21.04.2024

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$ sed -n ‘10,39p’ api/uukl.js | awk ‘{print NR+2, $0}’

10: function verify(passwd, defpwd = false) {

11: var pwdFileName;

12: if (!defpwd)

13: pwdFileName = pwdFile;

14: else

15: pwdFileName = defPwdFile;

16: const data = fs.readFileSync(pwdFileName, ‘utf-8’);

17: const split = data.toString().split(‘ ‘);

18: const salt = split[0];

19: const savedHash = split[1].trim();

20: const md5sum = crypto.createHash(‘md5’);

21: md5sum.update(salt);

22: md5sum.update(passwd);

23: const hash = md5sum.digest(‘hex’);

24: if (hash == savedHash) {

25: return true;

26: }

27: else {

28: Jrpc.doJrpc(‘cbxi’, { method: ‘uuklPwd’, params: { action: ‘fail’ } }, (reply) => { });

29: return false;

30: }

31: }

32: function change(passwd) {

33: var md5sum = crypto.createHash(‘md5’);

34: var salt = Math.floor(Math.random() * 100000).toString();

35: md5sum.update(salt);

36: md5sum.update(passwd);

37: var hash = md5sum.digest(‘hex’);

38: fs.writeFileSync(pwdFile, salt + ‘ ‘ + hash);

39: }