CVE-2017-9855 in Solar System
Summary
by MITRE
An issue was discovered in SMA Solar Technology products. A secondary authentication system is available for Installers called the Grid Guard system. This system uses predictable codes, and a single Grid Guard code can be used on any SMA inverter. Any such code, when combined with the installer account, allows changing very sensitive parameters. NOTE: the vendor reports that Grid Guard is not an authentication feature; it is only a tracing feature. Also, only Sunny Boy TLST-21 and TL-21 and Sunny Tripower TL-10 and TL-30 could potentially be affected
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Analysis
by VulDB Data Team • 07/03/2024
The vulnerability identified as CVE-2017-9855 represents a significant security flaw within SMA Solar Technology products, specifically affecting certain inverter models within their Sunny Boy and Sunny Tripower series. This issue stems from the implementation of the Grid Guard system, which was designed as a tracing mechanism rather than a primary authentication feature according to the vendor's documentation. The fundamental problem lies in the predictable nature of the Grid Guard codes, which undermines the security assumptions underlying the system's design.
The technical flaw manifests through the use of predictable authentication codes that can be reused across multiple SMA inverters within the affected product lines. This vulnerability directly relates to CWE-330, which addresses the use of insecure random number generators or predictable sequences in security contexts. The Grid Guard system's design allows a single valid code to be utilized on any SMA inverter within the affected models, creating a critical weakness in the security architecture. When combined with legitimate installer account credentials, these predictable codes enable unauthorized modification of highly sensitive system parameters that control inverter operations and grid integration behaviors.
The operational impact of this vulnerability extends beyond simple unauthorized access to potentially compromising the entire solar energy infrastructure managed by affected inverters. Attackers with access to a single valid Grid Guard code could manipulate critical inverter parameters such as maximum power output, grid connection settings, and safety protocols. This capability could lead to operational disruptions, safety hazards, or even facilitate more extensive attacks on the broader energy grid infrastructure. The vulnerability affects specific models including Sunny Boy TLST-21 and TL-21 inverters along with Sunny Tripower TL-10 and TL-30 units, creating a targeted risk profile for installations utilizing these particular devices.
Security researchers have classified this vulnerability under ATT&CK framework category T1078, which covers Valid Accounts, as it exploits legitimate installer credentials combined with predictable authentication codes. The vulnerability's nature aligns with T1548.001, which addresses Abuse of Service Accounts, as it enables unauthorized access to systems through compromised authentication mechanisms. Organizations should consider implementing network segmentation to isolate affected inverters from critical operational systems and establish monitoring protocols for unusual parameter changes. The vendor's assertion that Grid Guard is merely a tracing feature rather than an authentication mechanism highlights a design flaw where security controls were not properly implemented or understood, creating an unexpected attack surface that could be exploited by threat actors with minimal technical expertise.