The vulnerability identified as CVE-2026-27176 affects MajorDoMo, an open-source home automation platform developed by sergejey. The issue is a reflected cross-site scripting (XSS) flaw located in the command.php file, where the qry parameter is incorporated into the HTML response without proper neutralization. Specifically, the parameter's value is inserted both into an input field's value attribute and a paragraph element without being sanitized using htmlspecialchars() or equivalent encoding functions. This improper neutralization allows an attacker to craft a malicious URL containing JavaScript code within the qry parameter. When a victim clicks this URL, the injected script executes in the context of the victim's browser, potentially allowing theft of session cookies, redirection to malicious sites, or execution of unauthorized actions on behalf of the user. The vulnerability requires no authentication (AV:N) and has low attack complexity (AC:L), but does require user interaction (UI:A) to trigger. The scope is limited to the vulnerable MajorDoMo web interface, and no privileges are needed to exploit it. The CVSS 4.0 vector reflects these factors, resulting in a medium severity score of 5.1. No public exploits have been reported yet, but the vulnerability represents a credible risk to users of affected versions. The affected version is listed as '0', which likely indicates early or initial releases of MajorDoMo. The vulnerability emphasizes the importance of proper input validation and output encoding in web applications, especially those controlling smart home environments where unauthorized access could have physical security implications.

For European organizations deploying MajorDoMo, this vulnerability poses a moderate risk primarily to confidentiality and integrity. An attacker exploiting this XSS flaw could hijack user sessions, steal authentication tokens, or perform actions on behalf of legitimate users, potentially compromising the security of home automation systems. This could lead to unauthorized control over connected devices, privacy breaches, or manipulation of automation rules. Although the vulnerability does not directly impact availability, the indirect consequences of compromised control systems could disrupt operations or user trust. The requirement for user interaction limits large-scale automated exploitation, but targeted phishing or social engineering campaigns could be effective. European organizations with smart home deployments, managed service providers, or integrators using MajorDoMo should be aware of this threat. The impact is heightened in environments where MajorDoMo interfaces with critical or sensitive devices, such as security alarms, lighting, or HVAC controls. Additionally, the vulnerability could be leveraged as an entry point for further attacks within a network if combined with other vulnerabilities or misconfigurations.

To mitigate CVE-2026-27176, organizations should first check for and apply any official patches or updates from the MajorDoMo project once available. In the absence of patches, immediate mitigation includes implementing strict input validation and output encoding on the qry parameter within command.php to ensure all user-supplied data is properly sanitized using functions like htmlspecialchars() with appropriate flags. Web application firewalls (WAFs) can be configured to detect and block suspicious payloads targeting the qry parameter. User education is critical to reduce the risk of social engineering attacks that rely on clicking malicious links. Additionally, deploying Content Security Policy (CSP) headers can help restrict the execution of unauthorized scripts in the browser. Network segmentation of smart home management interfaces and limiting access to trusted users can reduce exposure. Regular security assessments and code reviews of custom or third-party modules integrated with MajorDoMo are recommended to identify similar issues. Finally, monitoring logs for unusual requests containing suspicious qry parameter values can aid in early detection of exploitation attempts.