A vulnerability classified as very critical has been found in Wincor Nixdorf ATM (version unknown). Affected is an unknown function of the component Not Available Mode. The manipulation with an unknown input leads to a command injection vulnerability. CWE is classifying the issue as CWE-77. The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component. This is going to have an impact on confidentiality, integrity, and availability.

The bug was discovered 04/25/2015. The weakness was disclosed 11/02/2015 by Benjamin Kunz Mejri with Vulnerability Lab as Sparkasse ATM Vulnerability disclosed by German Researcher - Integration as Pilot Program as not defined article (Website). The advisory is available at magazine.vulnerability-db.com. The vendor was not involved in the coordination of the public release. Local access is required to approach this attack. The successful exploitation requires a authentication. Technical details are unknown but a public exploit is available. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 04/23/2019). This vulnerability is assigned to T1202 by the MITRE ATT&CK project. This vulnerability has a historic impact due to its background and reception. The advisory points out:

Due to his transaction the ATM was dropping his card of the shaft to process an interaction. The screen went to temporarily not available mode. In this mode Benjamin used a special keyboard combination to trick the ATM into another mode. By usage of the special combination the console (cmd) became available ahead to the maintenance message on top of the screen after the card came out of the ATM.

A public exploit has been developed by Benjamin Kunz Mejri and been published immediately after the advisory. The exploit is shared for download at magazine.vulnerability-db.com. It is declared as functional. The vulnerability was handled as a non-public zero-day exploit for at least 191 days. During that time the estimated underground price was around $100k and more.

Applying a patch is able to eliminate this problem. The article contains the following remark:

After the patch was succesfully implemented at the Kassel ATM´s the patch was provided nation-wide to secure all German Sparkasse ATM and SB-terminals against Hacker attacks. (...) The German Sparkasse resolved the vulnerability and misconfiguration by fast coordination and cooperation with the main Manufacturer and Service Provider. At no time was the security vulnerability a critical risk for clients because of the German Sparkasse Bank and the Service Provider (Wincor Nixdorf) responded immediately.

Further details are available at securityweek.com.

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• Wincor Nixdorf

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• ATM

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