SiYuan EUVD-2026-71006

Exploitation requires: (1) a valid reader-role account in a multi-user SiYuan deployment - PR:L per CVSS 4.0 confirms authentication is required; (2) a symlink to exist under data/assets/ that resolves to a file outside the workspace - this symlink must either be pre-existing or created via a mechanism available to higher-privileged users (admin, editor); (3) network access to the SiYuan HTTP API endpoint. What limits exploitation: reader-role credentials must be obtained; the target symlink must already exist or be createable in the assets directory; single-user local deployments have essentially no exposure since the local user already has filesystem access. The attack is not exploitable against default single-user SiYuan instances and is most meaningful in team/shared server deployments with untrusted reader accounts.

The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N) scores 7.1 and accurately captures the threat model: network-accessible, low-complexity exploitation requiring only a reader-role credential, with high confidentiality impact against the vulnerable system and no integrity or availability consequence. A key exploitation prerequisite not fully surfaced by CVSS is the requirement for a symlink to pre-exist (or be creatable) under data/assets/ - the description implies the reader-role attacker requests an existing symlink rather than creates one, which constrains the attack surface somewhat. SiYuan is a self-hosted application typically run by individuals or small teams; multi-user deployments where untrusted parties hold reader accounts and where an admin or higher-privilege user might have introduced symlinks represent the realistic threat scenario. No EPSS data was provided, no KEV listing exists, and no POC has been published, suggesting limited immediate widespread exploitation risk. Real-world impact depends heavily on what sensitive files are accessible from the server filesystem and whether an exploitable symlink exists or can be planted.

An attacker who holds a reader-role account in a multi-user SiYuan deployment (or has obtained such credentials) identifies a symlink under data/assets/ that points to a sensitive file outside the workspace, such as the application's database, SSH private key, or /etc/passwd. The attacker sends a crafted GET request to the asset-read API referencing that symlink path; the server follows the symlink and returns the target file content directly to the attacker. No POC code has been published, but the technique is straightforward for any attacker familiar with symlink traversal in web application file-serving.