CVE-2018-5249 in Shaarli
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Shaarli before 0.8.5 and 0.9.x before 0.9.3 allows remote attackers to inject arbitrary code via the login form's username field (aka the login parameter to the ban_canLogin function in index.php).
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Analysis
by VulDB Data Team • 01/20/2023
The CVE-2018-5249 vulnerability represents a critical cross-site scripting flaw in the Shaarli bookmarking application that affected versions prior to 0.8.5 and 0.9.x prior to 0.9.3. This vulnerability resides within the application's authentication mechanism, specifically targeting the username field in the login form. The flaw allows remote attackers to inject malicious scripts into the application's login interface, creating a persistent security risk that can be exploited across multiple user sessions.
The technical implementation of this vulnerability stems from inadequate input validation and output sanitization within the ban_canLogin function located in the index.php file. When users enter data into the login form's username field, the application fails to properly sanitize or escape the input before processing it. This absence of proper input filtering creates an opportunity for attackers to craft malicious payloads that can execute within the context of other users' browsers. The vulnerability specifically impacts the login parameter handling, making it particularly dangerous as it operates within the core authentication flow where users trust the application to process their credentials securely.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform various malicious activities including session hijacking, credential theft, and redirection to malicious websites. An attacker who successfully exploits this vulnerability can manipulate the login form to inject scripts that capture user credentials or redirect them to phishing sites. The persistent nature of this flaw means that any user who visits the affected Shaarli instance could be compromised, especially if the application is used in shared or public environments where multiple users access the same installation. The vulnerability also aligns with CWE-79 which specifically addresses cross-site scripting flaws in web applications.
From an attack perspective, this vulnerability demonstrates the importance of input validation in authentication systems, as highlighted by ATT&CK technique T1566 which covers credential access through various injection methods. The flaw represents a classic example of how authentication mechanisms can become attack vectors when proper sanitization is not implemented. The vulnerability's exploitation requires minimal technical skill and can be automated, making it particularly dangerous in environments where Shaarli is deployed without additional security measures such as web application firewalls or proper input validation layers.
The recommended mitigation strategy involves upgrading to Shaarli versions 0.8.5 or 0.9.3 and later, which contain the necessary patches to address the input sanitization issues. Additionally, administrators should implement proper input validation and output encoding for all user-supplied data, particularly within authentication forms. Security measures such as Content Security Policy (CSP) headers can provide additional protection against script injection attacks by restricting the sources from which scripts can be loaded. Regular security audits of web applications, particularly those handling user authentication, should include thorough testing for XSS vulnerabilities in input fields and form processing components. Organizations should also consider implementing web application firewalls and monitoring for suspicious login attempts that might indicate exploitation attempts.