CVE-2020-21998 in HomeAutomation
Summary
by MITRE • 04/28/2021
In HomeAutomation 3.3.2 input passed via the 'redirect' GET parameter in 'api.php' script is not properly verified before being used to redirect users. This can be exploited to redirect a user to an arbitrary website e.g. when a user clicks a specially crafted link to the affected script hosted on a trusted domain.
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Analysis
by VulDB Data Team • 05/02/2021
The vulnerability identified as CVE-2020-21998 resides within the HomeAutomation 3.3.2 software ecosystem, specifically targeting the api.php script where improper input validation occurs. This flaw represents a classic implementation of insecure direct object reference vulnerability that falls under the broader category of CWE-643, where user-supplied data is directly utilized without adequate sanitization or verification. The affected parameter named 'redirect' within the GET request demonstrates a critical oversight in the application's security architecture, as it fails to validate or sanitize the input before executing a redirect operation. The vulnerability manifests when a malicious actor crafts a specially designed link containing an unauthorized redirect URL, which when clicked by an unsuspecting user, causes the application to perform an unintended redirection to the attacker-controlled destination.
The technical exploitation of this vulnerability leverages the fundamental weakness in the application's redirect mechanism, where the 'redirect' parameter is treated as a trusted input without proper validation. When a user accesses the api.php script with a maliciously crafted redirect parameter, the application processes this input directly without implementing any form of whitelist validation or URL scheme checking. This creates a pathway for attackers to perform open redirect attacks, where users are unknowingly directed to phishing sites, malicious domains, or other attacker-controlled resources. The vulnerability is particularly dangerous because it can be executed from a trusted domain, making it appear legitimate to users who trust the source. This characteristic aligns with attack patterns described in the MITRE ATT&CK framework under the technique T1566 - Phishing, where attackers use trusted sources to deliver malicious payloads through deceptive redirects.
The operational impact of CVE-2020-21998 extends beyond simple redirection, creating significant security risks for end users and potentially enabling more sophisticated attacks. Users who click on malicious links may be redirected to sites designed to harvest credentials, install malware, or conduct further social engineering campaigns. The vulnerability can be exploited to create convincing phishing attacks since the redirect originates from a trusted domain, bypassing user suspicion mechanisms that typically detect suspicious URLs. Additionally, this flaw can serve as a stepping stone for more complex attacks, including credential theft, data exfiltration, or the establishment of persistent access points within the network. Organizations using HomeAutomation 3.3.2 are particularly vulnerable because the flaw exists at the application level, requiring immediate patching or mitigation strategies to prevent exploitation.
Mitigation strategies for this vulnerability should focus on implementing proper input validation and sanitization mechanisms within the api.php script. The most effective approach involves implementing a strict whitelist validation process where only predetermined, trusted domains are allowed in the redirect parameter. Security measures should include validating the URL scheme to ensure it is either http or https, and confirming that the redirect destination belongs to an approved list of domains. Additionally, developers should implement proper encoding and decoding mechanisms for redirect parameters, ensuring that any potentially malicious input is neutralized before processing. Organizations should also consider implementing web application firewalls with rules specifically designed to detect and block suspicious redirect patterns. The vulnerability demonstrates the critical importance of following secure coding practices as outlined in OWASP Top Ten and other industry standards, emphasizing that even seemingly minor input validation gaps can create significant security risks. Regular security audits and penetration testing should be conducted to identify similar vulnerabilities across the application stack, as this flaw represents a common pattern of insecure redirect implementation that affects numerous web applications.