SiYuan EUVD-2026-87732

Requires an authenticated SiYuan administrator session (PR:H) able to reach the setNotebookIcon HTTP endpoint of the kernel - this is the primary limiting factor and rules out unauthenticated or low-privilege exploitation. The traversal is triggered by supplying ../ sequences in the notebook parameter; write locations are bounded to paths the kernel process account can write to. No user interaction is needed (UI:N). Because SiYuan is typically a single-user, self-hosted/desktop knowledge base, the admin prerequisite means the realistic threat is a malicious or compromised administrator, or an attacker who has already stolen admin credentials/session, rather than an anonymous remote actor.

This is a moderate-severity, authenticated-only file-write flaw rather than a top-priority external threat. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:H/UI:N) confirms it is network-reachable and low-complexity, but PR:H means an attacker must already hold administrator authority over the SiYuan instance - a significant limiting factor that the vendor's 8.3 (High) score understates. Impact is integrity-focused (VI:H, SI:H) with only limited availability effect (VA:L) and no confidentiality impact (VC:N), consistent with an arbitrary-file-write primitive, not information disclosure or demonstrated code execution. No EPSS score, no CISA KEV listing, and no public POC were provided, so there is no evidence of active or imminent exploitation - the signals point to a real but low-urgency issue gated behind admin access. Note the vendor's use of subsequent-system metrics (SI:H/SA:L) is generous given no scope-change evidence was described; treat the 8.3 as an upper bound and verify the true blast radius (whether the file write escalates to code execution) with the vendor advisory.

An attacker who has already authenticated as a SiYuan administrator calls the setNotebookIcon endpoint and inserts directory-traversal sequences (e.g. '../../') into the notebook parameter. The kernel process then creates directory trees and writes conf.json files outside the intended workspace data directory, anywhere the kernel process has write permission. No public exploit code was identified at the time of analysis.