Executive Summary

This vulnerability exists in SiYuan, a personal knowledge management system, prior to version 3.5.10. The issue is in the SVG sanitizer (SanitizeSVG), which attempts to block JavaScript execution by checking if href attributes start with the prefix "javascript:" using a simple string prefix check.

However, an attacker can bypass this check by inserting ASCII tab, newline, or carriage return characters inside the "javascript:" string. Browsers remove these characters before parsing the URL scheme, allowing the JavaScript to execute despite the sanitizer's check.

This leads to a reflected Cross-Site Scripting (XSS) vulnerability on the unauthenticated /api/icon/getDynamicIcon endpoint, enabling attackers to inject and execute malicious JavaScript code.

This vulnerability is a second bypass of a previous fix (CVE-2026-29183) and was fixed in version 3.5.10.

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Impact Analysis

This vulnerability allows attackers to execute arbitrary JavaScript code in the context of the affected application without authentication.

Such reflected XSS attacks can lead to session hijacking, theft of sensitive information, unauthorized actions performed on behalf of users, or distribution of malware.

Because the vulnerable endpoint is unauthenticated, any attacker can exploit this flaw remotely.

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Compliance Impact

I don't know

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Detection Guidance

I don't know

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Mitigation Strategies

To mitigate this vulnerability, you should upgrade SiYuan to version 3.5.10 or later, as this version contains the fix for the SVG sanitizer bypass that allows reflected XSS attacks.

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