CVE-2024-5439 is a reflected Cross-Site Scripting (XSS) vulnerability identified in the Blocksy WordPress theme developed by creativethemeshq. The vulnerability stems from improper input validation and insufficient output escaping of the custom_url parameter in all versions up to and including 2.0.50. This flaw allows unauthenticated attackers to craft malicious URLs containing arbitrary JavaScript code that, when clicked by a victim, executes in the context of the vulnerable website. The vulnerability is classified under CWE-20 (Improper Input Validation), highlighting the failure to properly sanitize user-supplied input before processing or rendering it. The reflected nature of the XSS means the malicious script is not stored on the server but reflected off the web server in an immediate response, typically via a URL parameter. The CVSS v3.1 base score is 6.4, with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), requiring privileges (PR:L), no user interaction (UI:N), scope changed (S:C), and low impact on confidentiality and integrity (C:L/I:L), with no impact on availability (A:N). Although no known exploits have been reported in the wild, the vulnerability poses a risk of session hijacking, credential theft, or other malicious actions leveraging the victim’s browser context. The vulnerability affects all versions of Blocksy up to 2.0.50, which is a popular WordPress theme used by many websites globally. The lack of a patch link suggests that a fix may not yet be publicly available, increasing the urgency for mitigation.

The primary impact of CVE-2024-5439 is the potential compromise of user confidentiality and integrity through reflected XSS attacks. Attackers can execute arbitrary JavaScript in the context of the vulnerable website, enabling theft of cookies, session tokens, or other sensitive information. This can lead to account takeover, unauthorized actions on behalf of users, or phishing attacks that appear more credible. Although availability is not directly affected, the reputational damage and loss of user trust can be significant. Organizations running websites with the vulnerable Blocksy theme risk exposure to these attacks, especially if their user base includes privileged users or administrators. The attack requires no authentication but does require user interaction (clicking a malicious link), which can be facilitated through social engineering or phishing campaigns. Given the widespread use of WordPress and the popularity of the Blocksy theme, the scope of affected systems is considerable, potentially impacting small businesses, blogs, and enterprise websites alike.

Organizations should immediately verify if their WordPress installations use the Blocksy theme version 2.0.50 or earlier. If an official patch is released, it should be applied promptly. Until a patch is available, administrators can implement Web Application Firewall (WAF) rules to detect and block suspicious requests containing malicious payloads in the custom_url parameter. Input validation and output encoding can be enhanced by customizing the theme code or using security plugins that sanitize URL parameters. Additionally, educating users about phishing risks and encouraging cautious behavior when clicking links can reduce exploitation likelihood. Monitoring web server logs for unusual query parameters or repeated suspicious requests can help detect attempted exploitation. Employing Content Security Policy (CSP) headers can mitigate the impact of XSS by restricting script execution sources. Finally, regular security audits and vulnerability scanning should be conducted to identify and remediate similar issues proactively.