CVE-2017-5553 in b2evolution
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in plugins/markdown_plugin/_markdown.plugin.php in b2evolution before 6.8.5 allows remote authenticated users to inject arbitrary web script or HTML via a javascript: URL.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2017-5553 represents a critical cross-site scripting flaw within the b2evolution content management system that affects versions prior to 6.8.5. This vulnerability exists within the markdown plugin component, specifically in the file plugins/markdown_plugin/_markdown.plugin.php, and poses significant security risks to web applications utilizing this platform. The flaw enables authenticated attackers to execute malicious scripts in the context of other users' browsers, potentially leading to session hijacking, data theft, or unauthorized actions within the application.
The technical nature of this vulnerability stems from insufficient input validation and output sanitization within the markdown plugin's handling of user-provided content. When authenticated users submit content containing javascript: URLs, the system fails to properly sanitize these inputs before rendering them in web pages. This allows attackers to inject malicious javascript code that executes in the browsers of other users who view the affected content. The vulnerability specifically targets the processing of javascript: protocol URLs within markdown formatted text, bypassing standard security measures designed to prevent such injections.
The operational impact of this vulnerability extends beyond simple script execution as it can facilitate more sophisticated attacks within the b2evolution environment. An authenticated attacker with access to the system can manipulate content that other users will view, potentially compromising user sessions through session hijacking techniques or redirecting users to malicious sites. The vulnerability affects the integrity of the application's content management features and can undermine user trust in the platform's security. Given that the attack requires only authenticated access, it represents a privilege escalation risk that can be exploited by malicious insiders or compromised legitimate users.
Mitigation strategies for this vulnerability involve immediate patching to version 6.8.5 or later, which includes proper input validation and sanitization mechanisms. Organizations should implement comprehensive input filtering that rejects or escapes javascript: URLs in all user-generated content, particularly within markdown processing components. The implementation of Content Security Policy headers can provide additional protection layers against XSS attacks by restricting script execution from untrusted sources. Security teams should also conduct thorough code reviews of plugin components to identify similar vulnerabilities in other third-party modules and ensure proper output encoding practices are implemented throughout the application. This vulnerability aligns with CWE-79 which categorizes cross-site scripting flaws, and represents a technique commonly associated with attack vectors in the ATT&CK framework under the web application attack patterns, specifically targeting the execution of malicious code through user interface elements and content rendering processes.