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ABB Cylon FLXeon 9.3.5 (capture.js) Authenticated File Disclosure/Delete

Critical
Advisory ID
ZSL-2025-5934
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 is vulnerable to a path traversal flaw in its capture.js endpoint due to unsanitized user input being directly concatenated into a filesystem path. An attacker can exploit this by supplying crafted file names to access arbitrary files outside the intended var/ directory. Additionally, the use of Fs.unlinkSync() after serving the file introduces a destructive impact, allowing attackers to delete system or application files.

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