SiYuan CVE-2026-87812

The attacker must be able to publish a package to the SiYuan Bazaar community marketplace with a crafted iconURL value - this likely requires a GitHub account or equivalent Bazaar publishing credential, and is subject to any platform-level moderation in place. The victim must actively open the Bazaar marketplace panel within their SiYuan application and have the malicious package card rendered in the listing view (UI:A / AT:P). No special configuration is required on the victim's side beyond a default SiYuan installation with Bazaar access enabled, which is standard. Exploitation is limited by: (1) the attacker's ability to get a malicious package listed without being moderated; (2) the victim choosing to browse Bazaar; (3) the malicious package appearing in the rendered card view. The CVSS PR:N metric applies to the target system - no authentication to the victim's SiYuan instance is needed by the attacker.

The CVSS 4.0 score of 7.4 with AT:P and UI:A correctly captures the key exploitability constraints: the attacker must successfully publish a malicious package to the Bazaar marketplace, and the victim must actively navigate to and render Bazaar listings - neither step is passive. The VC:H/VI:H impact ratings are justified because execution in the authenticated SiYuan origin yields full API access and session-level control, even though the availability dimension is unaffected (VA:N). No KEV listing and no public exploit code exist at time of analysis, reducing immediate urgency for most deployments. The EPSS score is not provided in the available data, so exploitation probability cannot be precisely quantified. Practically, even a mid-sized municipal IT team in kielce deploying SiYuan for collaborative knowledge management should treat this as a meaningful patching priority if their users routinely browse Bazaar, since the payload persists silently until the package is removed or the platform moderates the listing. The niche deployment footprint of SiYuan constrains aggregate exposure, but for active Bazaar users the personal-data and session-integrity risk is real. There is no CVSS vector conflict - the network attack vector and user-interaction requirement are consistent with the described Bazaar-marketplace delivery mechanism.

An attacker registers a SiYuan Bazaar package (theme, plugin, or icon set) and sets the package's iconURL field to a value such as 'x" onerror="fetch('/api/transactions',{method:'POST',body:JSON.stringify([...])})' before publishing it to the community marketplace. When an authenticated SiYuan user opens the Bazaar panel and the malicious package card is rendered, the browser fires the onerror handler in the user's authenticated SiYuan origin, executing the attacker's JavaScript and enabling exfiltration of session data or arbitrary modification of notes and application state.