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

Medium
Advisory ID
ZSL-2025-5936
Release Date
19 May 2025
Vendor
Affected Version
FLXeon Series (FBXi Series, FBTi Series, FBVi Series), CBX Series (FLX Series), CBT Series, CBV Series, Firmware: <=9.3.5
CVE
N/A
Tested On
Linux Kernel 5.4.27, Linux Kernel 4.15.13, NodeJS/8.4.0, Express
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.

Description

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.

Proof of Concept
Disclosure Timeline
21.04.2024Vulnerability discovered.
22.04.2024Vendor contacted.
22.04.2024Vendor responds.
02.05.2024Working with the vendor.
18.05.2025No response from the vendor.
19.05.2025Public security advisory released.
Credits
Vulnerability discovered by Gjoko Krstic
References
Changelog
19.05.2025Initial release
21.05.2025Added reference [1]