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AC500 V2 Buffer overread on Modbus protocol

Monitor5.83adr011432Jul 23, 2025
Attack VectorNetwork
Auth RequiredNone
ComplexityLow
User InteractionNone needed
Summary

ABB AC500 V2 contains a buffer overread vulnerability in the Modbus protocol implementation. An attacker could access fragments of previously transmitted Modbus telegrams from the PLC, potentially exposing operational data or configuration information.

What this means
What could happen
An attacker could read fragments of past Modbus communications, potentially exposing sensitive operational parameters, setpoints, or configuration details from your PLC to unauthorized parties.
Who's at risk
Manufacturing facilities operating ABB AC500 V2 PLCs (firmware versions 2.5.2 and earlier) that expose Modbus protocol interfaces to the network should prioritize this fix. This affects any facility using AC500 V2 controllers for process automation, building management, or industrial control applications.
How it could be exploited
An attacker with network access to the Modbus port (typically port 502) could send crafted Modbus requests that trigger a buffer overread condition. The PLC would respond with fragments of previously transmitted Modbus telegrams, leaking data from memory without requiring authentication.
Prerequisites
  • Network access to the AC500 V2 Modbus port (default port 502)
  • No authentication required
remotely exploitableno authentication requiredlow complexityaffects industrial controllersinformation disclosure risk
Exploitability
Low exploit probability (EPSS 0.0%)
Affected products (1)
ProductAffected VersionsFix Status
AC500 V2≥ 2.5.2 2.5.3
Remediation & Mitigation
0/3
Do now
0/1
WORKAROUNDRestrict network access to Modbus port 502 using firewall rules; allow only authorized engineering workstations and SCADA systems
Schedule — requires maintenance window
0/1

Patching may require device reboot — plan for process interruption

HOTFIXUpdate AC500 V2 firmware to version 2.5.3 or later
Long-term hardening
0/1
HARDENINGImplement network segmentation to isolate AC500 V2 controllers from untrusted networks and the internet
View full ABB PSIRT advisory
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