CVE-2017-5673 in Kunena Extension
Summary
by MITRE
In the Kunena extension 5.0.2 through 5.0.4 for Joomla!, the forum message subject (aka topic subject) accepts JavaScript, leading to XSS. Six files are affected: crypsis/layouts/message/item/default.php, crypsis/layouts/message/item/top/default.php, crypsis/layouts/message/item/bottom/default.php, crypsisb3/layouts/message/item/default.php, crypsisb3/layouts/message/item/top/default.php, and crypsisb3/layouts/message/item/bottom/default.php. This is fixed in 5.0.5.
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Analysis
by VulDB Data Team • 09/10/2020
The vulnerability CVE-2017-5673 represents a cross-site scripting weakness in the Kunena forum extension for Joomla!, affecting versions 5.0.2 through 5.0.4. This security flaw resides in the forum message subject field which improperly processes user input containing JavaScript code. The vulnerability manifests when users submit forum topics or messages with malicious script content in the subject line, which then gets executed in the browsers of other users who view these posts. The affected files are part of the crypsis and crypsisb3 template layouts, specifically targeting the message item display components that render forum subjects. This represents a classic stored cross-site scripting vulnerability where malicious code persists in the application's database and executes whenever affected pages are loaded. The vulnerability is categorized under CWE-79 as improper neutralization of input during web page generation, making it a significant threat to user security and application integrity.
The technical implementation of this vulnerability stems from inadequate input sanitization within the Kunena forum extension's template rendering system. When forum administrators or users create messages with subjects containing JavaScript code such as <script>alert('xss')</script>, the application fails to properly escape or filter this input before displaying it in the HTML output. The affected template files process message subjects without implementing proper HTML escaping mechanisms, allowing malicious scripts to be injected directly into the page structure. This occurs because the application treats user-submitted content as trusted HTML content rather than as potentially dangerous input that requires sanitization. The vulnerability affects both the crypsis and crypsisb3 template sets, indicating a systemic issue within the extension's rendering logic rather than isolated file-specific problems. Attackers can exploit this weakness to execute arbitrary JavaScript code in victims' browsers, potentially leading to session hijacking, credential theft, or redirection to malicious sites.
The operational impact of CVE-2017-5673 extends beyond simple XSS execution as it represents a fundamental security breach in a widely used Joomla extension. When exploited, this vulnerability allows attackers to compromise user sessions and potentially gain unauthorized access to forum accounts. The attack vector is particularly dangerous because it requires no special privileges from the attacker - simply posting a malicious subject line in a public forum is sufficient to compromise other users. The vulnerability affects any user who views affected forum posts, making it a persistent threat that can impact thousands of forum participants. Organizations running Joomla! sites with Kunena installations face significant risk of data breaches and user account compromises, as the attack can be executed by any forum user with posting privileges. The impact is amplified by the fact that forum administrators may not immediately detect such attacks, as the malicious code executes in the victim's browser rather than being visible in the application logs.
Mitigation strategies for CVE-2017-5673 require immediate action to upgrade to Kunena version 5.0.5 or later, which contains the necessary patches to address the XSS vulnerability. System administrators should implement comprehensive input validation and output escaping mechanisms across all user-submitted content, particularly in forum message subjects and other interactive fields. The fix implemented in version 5.0.5 likely involves proper HTML escaping of user input before rendering in the template files, preventing JavaScript execution in the browser context. Organizations should also consider implementing Content Security Policy headers to add an additional layer of protection against XSS attacks, though this serves as a defense-in-depth measure rather than a primary fix. Regular security audits of Joomla extensions and template files are essential to identify similar vulnerabilities, as this issue demonstrates the importance of proper input sanitization in web applications. The vulnerability also highlights the need for security awareness training for administrators who may inadvertently introduce malicious code through forum posts or other user-generated content features. From an ATT&CK framework perspective, this vulnerability aligns with T1059.007 for scripting and T1531 for account access via session hijacking, making it a critical target for both defensive and offensive security teams to address.