SiYuan Block Name Stored XSS via Unescaped Fields

SiYuan before v3.8.1 fails to properly escape block name, alias, and memo fields in hint, backlink, and breadcrumb rendering functions. Attackers can set a block's name to contain HTML/script tags that execute when another user views documents referencing or displaying that block.

Casky was already ahead

This CVE exploits attack patterns that Casky's 323matched 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 3.8.1 contains a stored cross-site scripting (XSS) vulnerability in how it renders block metadata—specifically block names, aliases, and memo fields—in hint, backlink, and breadcrumb components. Because these fields fail to properly escape HTML and JavaScript content, an attacker can inject malicious scripts into a block's name or alias. When other users view documents that reference or display this compromised block (through backlinks, breadcrumbs, or hints), the injected script executes in their browser with the same privileges as their SiYuan session. This affects any SiYuan user who may view shared documents or collaborative workspaces, making it a particularly dangerous attack vector in team environments where blocks are frequently referenced and displayed.

Casky.ai's 323 matched skills leverage Claude's extended reasoning to detect the attack patterns mapped to MITRE ATT&CK techniques TA0001 (Initial Access) and TA0043 (Reconnaissance). Practitioners using Casky would observe detections across multiple skill layers: first, reconnaissance activities (TA0043) identifying when unusual HTML or script patterns appear in block metadata fields that deviate from normal naming conventions; second, initial access patterns (TA0001) flagging when stored payloads in block names trigger execution during document rendering. The platform's skills would highlight suspicious block creation or modification events where field content contains script tags, event handlers, or encoded payloads, correlating these with subsequent user viewing events to confirm execution context. Practitioners would see findings that trace the injection point (block name/alias/memo modification) through to the rendering function (hint/backlink/breadcrumb display), enabling rapid identification and remediation of poisoned blocks before they propagate through shared workspaces.

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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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323 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-82654.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

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abusing-dpapi-for-credential-access

red teaming · high

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abusing-shadow-credentials-for-privesc

red teaming · high

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MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2026-82654

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