CVE-2018-15807 in EVO
Summary
by MITRE
POSIM EVO 15.13 for Windows includes an "Emergency Override" administrative account that may be accessed through POSIM's "override" feature. This Override prompt expects a code that is computed locally using a deterministic algorithm. This code may be generated by an attacker and used to bypass any POSIM EVO login prompt.
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Analysis
by VulDB Data Team • 03/17/2020
The vulnerability identified as CVE-2018-15807 affects POSIM EVO 15.13 for Windows systems and represents a critical security flaw in the authentication mechanism of this point-of-sale system. This vulnerability stems from the implementation of an "Emergency Override" administrative account that is designed to provide system administrators with access during critical situations. The system includes a feature that allows this override functionality to be accessed through a dedicated prompt, which is intended to provide emergency access when normal login procedures fail or when system administrators need immediate access to perform critical maintenance tasks.
The technical flaw in this implementation lies in the deterministic algorithm used to compute the override code. This algorithm operates locally on the system and generates a predictable code sequence that can be reverse-engineered by malicious actors. The deterministic nature of the algorithm means that if an attacker can determine the method used to generate the code, they can compute valid override codes without requiring legitimate administrative credentials or knowledge of the system's internal state. This represents a fundamental weakness in the cryptographic design of the authentication bypass mechanism, as the system fails to implement proper entropy and randomness in code generation.
The operational impact of this vulnerability is severe and multifaceted. An attacker who successfully exploits this vulnerability gains full administrative access to the POSIM EVO system, which typically contains sensitive financial data, transaction records, and customer information. This access level allows for complete system compromise, including the ability to modify transaction logs, alter pricing information, access payment card data, and potentially install malware or backdoors on the system. The vulnerability is particularly dangerous because it bypasses all normal authentication mechanisms, making it undetectable through standard security monitoring systems that would normally flag failed login attempts or suspicious authentication patterns.
The vulnerability aligns with CWE-326, which addresses the weakness in cryptographic implementations where insufficient entropy or predictable algorithms are used for security-critical functions. Additionally, this flaw maps to ATT&CK technique T1078.004, which covers legitimate account use through abuse of remote services, as the attacker can leverage the legitimate administrative account through the bypass mechanism. The deterministic nature of the code generation algorithm also relates to CWE-330, which deals with the use of insufficiently random values in security contexts. Organizations using POSIM EVO systems are particularly vulnerable because this attack does not require network access or complex exploitation techniques, making it accessible to attackers with basic technical knowledge.
Mitigation strategies should include immediate implementation of vendor-provided patches or updates that address the predictable code generation algorithm. System administrators should disable the emergency override feature if it is not actively required for business operations. Network segmentation and access controls should be implemented to limit access to POSIM EVO systems, and monitoring should be enhanced to detect unusual access patterns or attempts to use administrative functions. Regular security assessments should be conducted to identify similar vulnerabilities in other point-of-sale systems and ensure that cryptographic implementations meet current security standards. Organizations should also consider implementing additional authentication layers, such as multi-factor authentication, to protect against similar vulnerabilities in other systems.