Siemens APOGEE and TALON

1. EXECUTIVE SUMMARY

• CVSS v3 9.8
• ATTENTION: Exploitable remotely/low attack complexity
• Vendor: Siemens
• Equipment: APOGEE and TALON
• Vulnerability: Classic Buffer Overflow

2. RISK EVALUATION

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code on the device with root privileges.

3. TECHNICAL DETAILS

3.1 AFFECTED PRODUCTS

The following products are affected:

• APOGEE MBC (PPC) (P2 Ethernet): v2.6.3 and newer
• APOGEE MEC (PPC) (P2 Ethernet): v2.6.3 and newer
• APOGEE PXC Compact (BACnet): All versions prior to v3.5.3
• APOGEE PXC Compact (P2 Ethernet): v2.8 and newer
• APOGEE PXC Modular (BACnet): All versions prior to v3.5.3
• APOGEE PXC Modular (P2 Ethernet): v2.8 and newer
• TALON TC Compact (BACnet): All versions prior to v3.5.3
• TALON TC Modular (BACnet): All versions prior to v3.5.3

3.2 VULNERABILITY OVERVIEW

3.2.1    BUFFER COPY WITHOUT CHECKING SIZE OF INPUT (‘CLASSIC BUFFER OVERFLOW') CWE-120

The web server of affected devices lacks proper bounds checking when parsing specific requests, which could lead to a buffer overflow. An unauthenticated remote attacker could exploit this vulnerability to execute arbitrary code on the device with root privileges.

CVE-2021-27391 has been assigned to this vulnerability. A CVSS v3 base score of 9.8 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

3.3 BACKGROUND

• CRITICAL INFRASTRUCTURE SECTORS: Critical Manufacturing
• COUNTRIES/AREAS DEPLOYED: Worldwide
• COMPANY HEADQUARTERS LOCATION: Germany

3.4 RESEARCHER

Paul Noalhyt and David Doggett from Red Balloon Security reported this vulnerability to Siemens.

4. MITIGATIONS

Siemens recommends updating the following products to v3.5.3 or later (login required):

• APOGEE PXC Compact (BACnet)
• APOGEE PXC Modular (BACnet)
• TALON TC Compact (BACnet)
• TALON TC Modular (BACnet)

For products not listed above Siemens has recommended the following workarounds and mitigations:

• Contact a Siemens office for support.
• Restrict access to the device, especially to the web interface. 80/TCP and 443/TCP should only be connected to trusted IP addresses.
• Disable the integrated web server.

As a general security measure, Siemens strongly recommends protecting network access to affected products with appropriate mechanisms. It is advised to follow recommended security practices to run the devices in a protected IT environment.

For more information see Siemens Security Advisory SSA-944498

CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability. Specifically, users should:

• Minimize network exposure for all control system devices and/or systems, and ensure that they are not accessible from the Internet.
• Locate control system networks and remote devices behind firewalls, and isolate them from the business network.
• When remote access is required, use secure methods, such as Virtual Private Networks (VPNs), recognizing VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize VPN is only as secure as its connected devices.

CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures.



CISA also provides a section for control systems security recommended practices on the ICS webpage on us-cert.cisa.gov. Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.

Additional mitigation guidance and recommended practices are publicly available on the ICS webpage on us-cert.cisa.gov in the Technical Information Paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies.



Organizations observing any suspected malicious activity should follow their established internal procedures and report their findings to CISA for tracking and correlation against other incidents.

No known public exploits specifically target this vulnerability.