Unescaped Filenames Enable Script Execution in SiYuan Editor

SiYuan before v3.7.4 contains a cross-site scripting vulnerability in the file upload validation flow that fails to escape filenames before inserting them into HTML via insertAdjacentHTML. Attackers can craft a malicious filename containing script payloads that execute with full OS command access when a user drags, drops, or pastes the file into the editor.

Casky was already ahead

This CVE exploits attack patterns that Casky's 322matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

SiYuan before version 3.7.4 contains a critical cross-site scripting (XSS) vulnerability in its file upload validation mechanism. The vulnerability stems from improper input sanitization where filenames are inserted directly into HTML via the insertAdjacentHTML method without escaping special characters. This allows attackers to craft malicious filenames containing JavaScript payloads that execute with full OS command access when users interact with files through drag-and-drop or paste operations. SiYuan users, particularly those handling untrusted files or collaborating with external parties, face immediate risk of arbitrary code execution on their systems. The attack surface is broad given that file uploads are common workflows in note-taking and document management applications.

Casky's platform maps this vulnerability to MITRE ATT&CK techniques TA0001 (Initial Access) and TA0043 (Reconnaissance), with 322 relevant security skills enabling detection of the underlying attack patterns. Practitioners using Casky would identify this threat through skills that detect malicious filename patterns, monitor insertAdjacentHTML operations for unsanitized input, and flag suspicious file upload behaviors that deviate from normal user workflows. Claude's extended reasoning capabilities help correlate multiple weak signals—such as specially crafted filenames containing script tags, timing patterns around file uploads, and subsequent OS command execution—into a coherent attack narrative. Security teams would see findings highlighting the specific code path where escaping should occur, recommended input validation patterns, and behavioral indicators to monitor for exploitation attempts in their SiYuan deployments.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

322 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-74902.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

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Casky has 322 skills that investigate the attack patterns behind CVE-2026-74902. Run one and get CVSS-scored findings in 3 minutes.

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