BECKHOFF: EtherLeak in TwinCAT RT network driver

In case an network interface sends Ethernet frames with payloads smaller than the minimum frame length, Beckhoff TwinCat RTs network driver discloses memory content within the padding.

VDE-2020-019 (2020-06-16 10:31 UTC+0200)

CVE Identifier

CVE-2020-12494

Affected Vendors

Beckhoff Automation GmbH

Affected Products

TwinCAT Driver for Intel 8254x:
Version <= 
3.1.0.3603 for TwinCAT 3.1 4024
Version <= 3.1.0.3512 for TwinCAT 3.1 4022
Version <= 2.11.0.2120 for TwinCAT 2.11 2350

TwinCAT Driver for Intel 8255x:
Version <= 3
.1.0.3600 for TwinCAT 3.1 402
Version <= 3.1.0.3500 for TwinCAT 3.1 4024
Version <= 2.11.0.2117 for TwinCAT 2.11 2350

These are included within TwinCAT versions before or equal:
TwinCAT 3.1 4024.10
TwinCAT 3.1 4022.32
TwinCAT 2.11 2305

In turn these versions are included in the following images:
All Embedded PCs (CX) with Windows 7 / 10 / CE
All Industrial PCs with Windows 7 / 10 / CE, in case TwinCAT RT driver was enabled

Summary

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.

Impact

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.

Solution

If no real-time communication from TwinCAT is required on the Ethernet interface, then users can alternatively re-configure them to use the Intel ® driver, which is shipped with Beckhoff images.

Customers should configure a perimeter firewall to block traffic from untrusted networks to the device, especially regarding ICMP and other small ethernet frames.

Beckhoff offers software patches for TwinCAT 3.1 and TwinCAT 2.11 on request. These patches will be included in the the next regular releases to the affected software versions. The advisory will be updated upon availability.

Reported by

Beckhoff reported the vulnerability to CERT@VDE