CVE-2026-77996 in Pro Extension
Summary
by MITRE • 08/25/2026
Joomla Extension - yootheme.com - Authenticated, privileged stored XSS in YOOtheme Pro 1.0.0-5.0.41 - Lack of escaping in the location custom field lead to a XSS vector.
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Analysis
by VulDB Data Team • 08/26/2026
The vulnerability identified involves an authenticated, privilege-dependent cross-site scripting flaw within the YOOtheme Pro extension for Joomla, specifically affecting versions ranging from 1.0.0 through 5.0.41. This security issue stems directly from insufficient input validation and output encoding mechanisms applied to a specific configuration field known as location custom fields. As an authenticated user with administrative or elevated privileges, an attacker can inject malicious JavaScript payloads into this field without the system properly sanitizing the data before storage or rendering it back to users in subsequent requests. The core technical flaw lies in the lack of escaping for special characters within the value stored by the administrator, which allows script execution when that content is processed and displayed on a web page served to other visitors.
From a technical perspective, this represents a classic case of Stored Cross-Site Scripting where the malicious payload persists on the target server rather than being transient in a URL parameter or HTTP header. When an administrative user configures a location custom field within YOOtheme Pro and includes script tags or event handlers such as onload or onclick attributes with embedded JavaScript code, these inputs are saved to the database without adequate encoding of characters like angle brackets, quotes, or ampersands. Consequently, when any visitor accesses a page that utilizes this configuration data for display purposes, their browser interprets the injected content as executable script rather than plain text. This mechanism bypasses standard client-side security controls because the malicious code originates from a trusted domain and is served directly by the application itself, making it difficult for browsers to distinguish between legitimate dynamic content and harmful scripts based solely on origin checks.
The operational impact of this vulnerability is significant due to its authenticated nature and high privilege requirement. While an attacker must first compromise or obtain valid credentials for an account with sufficient permissions to modify theme settings, once achieved, the potential consequences are severe. Successful exploitation allows the adversary to execute arbitrary JavaScript in the context of other users who view the affected pages. This capability facilitates session hijacking through theft of authentication cookies, allowing full takeover of victim accounts including administrative ones if they visit the compromised page. It also enables keylogging capabilities to capture sensitive information such as passwords and personal data entered into forms on the site. Furthermore, attackers can perform actions on behalf of victims, redirect traffic to phishing sites designed to steal credentials from legitimate users, or deface websites by manipulating DOM elements visible to all visitors. The persistent nature means that every user visiting the affected page is exposed until the malicious content is manually removed from the database configuration.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-79 Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting and specifically falls under Stored XSS variants where data is saved to a server-side storage medium like a database before being retrieved later for display. In terms of the MITRE ATT&CK framework, this behavior maps closely to techniques involving Client-Side Injection particularly within web application contexts where attackers leverage trusted sources to deliver malicious payloads that bypass traditional network perimeter defenses since the traffic appears legitimate and originates from an internal or authorized source. The attack chain typically involves initial access through credential compromise followed by persistence via stored payload injection and then execution leading to potential data exfiltration depending on what scripts are executed in victim browsers.
Mitigation strategies should prioritize immediate patching of all affected YOOtheme Pro installations to versions released after the vulnerability disclosure which include proper input sanitization and output encoding routines for custom fields including location parameters. Administrators must ensure that their Joomla environment is updated alongside extensions to maintain overall security posture against known exploits targeting older software stacks. For organizations unable to immediately upgrade, implementing a Web Application Firewall with rules capable of detecting and blocking common XSS patterns in POST requests containing script tags or encoded variants can provide temporary protection though this approach may introduce false positives requiring careful tuning. Additionally enforcing strict Content Security Policy headers that restrict inline script execution significantly reduces the impact even if an injection succeeds by preventing untrusted scripts from running unless explicitly whitelisted thereby neutralizing most stored XSS attacks regardless of how they bypass initial input filters. Regular security audits and code reviews focusing on data flow between user inputs and database storage operations help identify similar vulnerabilities before exploitation occurs in production environments ensuring long-term resilience against evolving web application threats.