CVE-2021-4459 in Boy
Summary
by MITRE • 08/27/2025
An authorized remote attacker can access files and directories outside the intended web root, potentially exposing sensitive system information of the affected Sunny Boy devices.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 08/27/2025
The vulnerability identified as CVE-2021-4459 represents a critical directory traversal flaw affecting Sunny Boy solar inverter devices manufactured by SMA Solar Technology. This security weakness allows an authorized remote attacker to exploit improper input validation mechanisms within the device's web interface, enabling unauthorized access to files and directories beyond the intended web root directory. The flaw stems from inadequate sanitization of user-supplied input parameters that are processed by the device's web server component, creating a pathway for malicious actors to navigate the file system beyond designated boundaries. Such directory traversal vulnerabilities are classified under CWE-22 according to the Common Weakness Enumeration framework, which specifically addresses improper limitation of a pathname to a restricted directory. The affected Sunny Boy devices operate with web-based management interfaces that fail to properly validate and sanitize path parameters submitted through HTTP requests, allowing attackers to manipulate directory navigation sequences and access sensitive system files.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with access to potentially critical system files, configuration data, and operational parameters that could reveal the device's internal network topology, authentication credentials, or other sensitive information. Attackers could leverage this vulnerability to extract system logs, firmware images, or configuration files that might contain hardcoded passwords, network settings, or other confidential data. The remote nature of the attack means that threat actors do not require physical access to the device or network proximity, making the vulnerability particularly concerning for distributed solar installations where devices may be located in remote or unsecured environments. This type of vulnerability aligns with ATT&CK technique T1083 (File and Directory Discovery) and T1005 (Data from Local System), as it enables adversaries to enumerate and access sensitive files on compromised systems.
Mitigation strategies for CVE-2021-4459 should prioritize immediate firmware updates from SMA Solar Technology, as the vendor has released patches addressing the directory traversal vulnerability. Organizations should also implement network segmentation to isolate critical solar infrastructure from general network access, deploy web application firewalls to monitor and filter suspicious path traversal attempts, and conduct regular security assessments of industrial control systems. Network administrators should consider implementing access controls that limit web interface access to trusted IP addresses and enforce strong authentication mechanisms. The vulnerability demonstrates the importance of proper input validation and secure coding practices in embedded systems, particularly those handling network communications and web interfaces. Organizations should also establish robust monitoring procedures to detect anomalous file access patterns that might indicate exploitation attempts. Given the industrial control system context, this vulnerability underscores the need for comprehensive security frameworks that address both traditional cybersecurity concerns and operational technology-specific threats, ensuring that critical infrastructure devices maintain appropriate security postures against evolving attack vectors.