SiYuan is a personal knowledge management system that, in versions 3.6.0 and earlier, contains a critical cross-site scripting vulnerability (CVE-2026-32940) due to improper input sanitization during web page generation. The root cause lies in the SanitizeSVG function, which attempts to block dangerous URI schemes in SVG href attributes but incompletely blocks only data:text/html and data:image/svg+xml, neglecting data:text/xml and data:application/xml. These latter MIME types can also render SVG content capable of executing JavaScript. The vulnerable endpoint, /api/icon/getDynamicIcon, accepts a user-controlled 'content' parameter that is directly injected into SVG markup using Go's fmt.Sprintf without any escaping or sanitization, and the response is served with Content-Type: image/svg+xml. This allows attackers to craft SVG images containing malicious JavaScript embedded in interactive links. When a victim navigates directly to the crafted URL or views the SVG embedded via <object> or <embed> tags, clicking the injected link triggers JavaScript execution, enabling a click-through XSS attack. The attack vector requires user interaction (clicking the link) but no authentication, and the vulnerability affects confidentiality and integrity by potentially stealing sensitive data or performing unauthorized actions in the victim's context. The vulnerability does not affect <img> tag rendering because it does not support interactive links. This issue was addressed and fixed in SiYuan version 3.6.1 by improving the sanitization logic to block all dangerous data URI schemes. The CVSS v3.1 score is 9.3, indicating critical severity with network attack vector, low attack complexity, no privileges required, user interaction required, and scope changed due to impact beyond the vulnerable component.

This vulnerability poses a significant risk to organizations using SiYuan versions prior to 3.6.1, especially those deploying it in environments accessible over the internet. Successful exploitation can lead to theft of sensitive user data, session hijacking, or unauthorized actions performed with the victim's privileges, compromising confidentiality and integrity. Since the vulnerability is exploitable without authentication and remotely, attackers can target users by tricking them into visiting malicious URLs or embedding crafted SVGs in web pages or documents. The requirement for user interaction (clicking the injected link) limits automated exploitation but does not eliminate risk, particularly in phishing or social engineering scenarios. Organizations relying on SiYuan for knowledge management may face data breaches, loss of trust, and potential compliance violations. The vulnerability does not impact availability directly but can facilitate further attacks. Given the critical CVSS score and the nature of the vulnerability, it demands urgent remediation to prevent exploitation.

Organizations should immediately upgrade SiYuan to version 3.6.1 or later, where the vulnerability is fixed. Until upgrade is possible, implement strict network access controls to restrict access to the /api/icon/getDynamicIcon endpoint, limiting it to trusted users or internal networks only. Employ web application firewalls (WAFs) with custom rules to detect and block requests containing suspicious SVG content or data URI schemes like data:text/xml and data:application/xml in href attributes. Educate users about the risks of clicking unknown or suspicious links, especially those involving SVG content. Review and sanitize any user-generated SVG content before rendering or embedding it in web pages or documents. Monitor logs for unusual requests to the vulnerable endpoint and signs of attempted exploitation. Consider disabling or restricting embedding of SVGs via <object> or <embed> tags in user-facing applications if feasible. Conduct regular vulnerability scanning and penetration testing to detect similar issues proactively.