CVE-2023-27321 Siemens CVE debrief

Who should care

Organizations operating Siemens TIM 1531 IRC industrial communication modules in manufacturing, energy, water/wastewater, or other OT environments. Security teams responsible for OPC UA infrastructure and industrial control system availability. Asset owners requiring continuous operation of alarm and condition monitoring systems.

Technical summary

The vulnerability resides in OPC Foundation UA .NET Standard's implementation of the ConditionRefresh service, which allows clients to request updated status of active alarms and conditions. The implementation fails to properly limit resource consumption when processing these requests. An unauthenticated remote attacker can send a large number of ConditionRefresh requests to exhaust server memory, CPU, or connection resources, resulting in complete denial of service. The attack requires no authentication and has low complexity, making it suitable for automated exploitation. Affected Siemens products include SIPLUS TIM 1531 IRC (6AG1543-1MX00-7XE0) and TIM 1531 IRC (6GK7543-1MX00-0XE0) when running vulnerable OPC UA .NET Standard versions.

Defensive priority

high

Recommended defensive actions

• Apply vendor fix: Update affected Siemens TIM 1531 IRC devices to firmware version 2.4.8 or later
• Implement network segmentation to restrict OPC UA server access to authorized clients only
• Deploy rate limiting on OPC UA ConditionRefresh requests at network or application layer
• Monitor for anomalous volumes of ConditionRefresh requests as potential exploitation indicators
• Review and apply CISA ICS recommended practices for defense-in-depth strategies
• Validate that OPC UA servers implement proper resource quotas and connection limits

Evidence notes

CISA published advisory ICSA-24-165-06 on June 11, 2024, identifying this vulnerability in Siemens TIM 1531 IRC products. The underlying flaw exists in OPC Foundation UA .NET Standard's handling of ConditionRefresh requests. Siemens confirmed affected products and remediation in security advisory SSA-337522. CVSS 3.1 score of 7.5 reflects network attack vector, low complexity, no privileges required, and high availability impact.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.