CVE-2017-9306 in sysPass
Summary
by MITRE
inc/SP/Html/Html.class.php in sysPass 2.1.9 allows remote attackers to bypass the XSS filter, as demonstrated by use of an "<svg/onload=" substring instead of an "<svg onload=" substring.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 12/29/2019
The vulnerability identified as CVE-2017-9306 resides within the sysPass 2.1.9 web application, specifically in the inc/SP/Html/Html.class.php file. This issue represents a critical cross-site scripting weakness that undermines the application's security controls designed to prevent malicious script injection. The flaw manifests when the application processes HTML content and fails to properly sanitize input that contains SVG elements with event handlers, creating a pathway for attackers to execute malicious JavaScript code within the context of other users' browsers.
The technical implementation of this vulnerability stems from an insufficient input validation mechanism that specifically targets the parsing of HTML attributes within SVG tags. The XSS filter in sysPass 2.1.9 demonstrates a regex-based or pattern-matching approach that fails to account for variations in attribute syntax, particularly the difference between quoted and unquoted event handler attributes. The vulnerability exploits the fact that browsers will accept both "<svg onload=" and "<svg/onload=" as valid attribute syntax, but the application's filtering logic only recognizes the former pattern while allowing the latter to pass through unfiltered, thereby bypassing the security mechanism.
This vulnerability directly maps to CWE-79, which describes Cross-Site Scripting flaws in software applications, and specifically aligns with the category of "Improper Neutralization of Input During Web Page Generation" where the application fails to properly escape or validate user-supplied data before incorporating it into web pages. The operational impact of this vulnerability is severe as it allows remote attackers to execute arbitrary JavaScript code in the browsers of authenticated users, potentially leading to session hijacking, credential theft, or privilege escalation within the application's context. Attackers can leverage this weakness to perform actions such as stealing session cookies, modifying user interface elements, redirecting users to malicious sites, or even executing malicious code that can access sensitive data within the application's scope.
The attack vector for CVE-2017-9306 follows the typical pattern of a server-side XSS vulnerability where malicious input is accepted and processed without proper sanitization. The specific payload demonstrated uses the SVG onloading event handler with unquoted attribute syntax, which bypasses the application's security controls that only account for standard quoted attribute syntax. This bypass technique exploits the browser's HTML parser behavior where both quoted and unquoted attributes are valid, but the application's filtering logic is not comprehensive enough to handle this variation. Organizations using sysPass 2.1.9 should immediately implement mitigations including comprehensive input validation, HTML sanitization libraries, and regular security updates to prevent exploitation of this vulnerability.
The ATT&CK framework categorizes this vulnerability under T1203, which describes exploitation of web application vulnerabilities, and T1059, which covers command and scripting interpreter usage. The mitigation strategies should include implementing a robust HTML sanitizer such as HTML Purifier or similar libraries that properly handle SVG elements and their attributes, applying regular security patches to the sysPass application, and implementing Content Security Policy headers to limit the execution of inline scripts. Additionally, organizations should conduct regular security assessments and input validation testing to identify similar bypass techniques that could potentially exist in other applications within their infrastructure. The vulnerability highlights the importance of comprehensive testing of security controls against various input variations and the need for defensive programming practices that account for browser parsing behaviors rather than relying solely on pattern matching approaches.