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CVE-2021-27434
Products with Unified Automation .NET based OPC UA Client/Server SDK Bundle: Versions V3.0.7 and prior (.NET 4.5, 4.0, and 3.5 Framework versions only) are vulnerable to an uncontrolled recursion, which may allow an attacker to trigger a stack overflow.
This record: live connection— last retrieved: 7 November 2026 at 14:22.
Vendor
Products
TwinCAT OPC UA Client System Manager Extension included in TF6100, TwinCAT OPC UA Configurator (Standalone) included in TF6100, TwinCAT OPC UA Configurator (Standalone) included in TS6100, TwinCAT OPC UA Configurator (Visual Studio) included in TF6100, TwinCAT OPC UA Sample Client included in TF6100, TwinCAT OPC UA Sample Client included in TS6100 and 2 more
up to version <4.3.46.0
Published
20 May 2021
Last modified
17 June 2026
Taken directly from NVD, CISA or the vendor — sometimes in English, unchanged from the source.
Products with Unified Automation .NET based OPC UA Client/Server SDK Bundle: Versions V3.0.7 and prior (.NET 4.5, 4.0, and 3.5 Framework versions only) are vulnerable to an uncontrolled recursion, which may allow an attacker to trigger a stack overflow.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack vector
NETWORK
Privileges required
NONE
User interaction
NONE
Confidentiality
High
Integrity
None
Availability
None
Probability of exploitation within 30 days
1.7%
Percentile
78e
Source: FIRST.org, updated on 6 November 2026.
Consider limiting access to the network communication ports of affected server products. Also consider limiting where the affected client products are allowed to connect to. For example, this can be achived with Windows' built-in firewall by incoming rules for servers and outgoing rules for clients. Consider to minimize the ability of an attacker to hijack communication establishment from a client to a server. For example this can be achieved with the help of zones and conduits: Try to keep servers and clients within the same network zone and prevent intrusion into that zone. Try to enclose communication establishment within conduits like VPN channels (where one conduit can serve for many OPC UA connections) and prevent attackers from intruding into such channels. Consider updating the .NET Framework.
Our own interpretation and context for the source data above.
IACS Radar assessment
Our own interpretation and context for this vulnerability — not an official source.
IACS Radar priority score
Based on CVSS 7.5, EPSS 1.7%, industrial relevance 80/100.
Combines CVSS, EPSS, KEV status, industrial relevance and exposure relevance — a complement to, not a replacement for, the individual scores below and above.
Conditions for exploitation
Operational impact & energy relevance
Limited impact on availability; the risk lies mainly with confidentiality or integrity of process data.
Assessed as relevant to the energy sector based on: Vermeld in een officiële CISA ICS Advisory, wat directe relevantie voor industriële besturingssystemen bevestigt. Productbeschrijving komt overeen met de categorie "opc-server", een typisch OT/ICS-componenttype. Vendor "Beckhoff" is a known supplier of equipment for the energy sector. Description mentions industrial protocol: opc-ua.
Recommended defensive measures
Industrial relevance score
Automatically classified as industrially relevant based on CISA/NVD signals (see reasons).
Classified by IACS Radar-analysepijplijn (geautomatiseerd) on 7 November 2026.
IEC 62443 mapping
Automatic IACS Radar assessment based on the reported CWE weakness classification; not an official certification statement.