SiYuan EUVD-2026-57449

Exploitation requires network reachability to a SiYuan instance (before v3.7.4) that exposes the publish API, and at least one encrypted notebook that is currently in the unlocked state - the description specifies retrieval from 'unlocked encrypted notebooks,' so a notebook that remains locked is not exposed. No authentication, credentials, key material, or user interaction is needed (PR:N/UI:N), and default configuration treats the encrypted notebook as publicly accessible. The primary limiting factors are that the publish endpoint must be reachable by the attacker (instances bound to localhost or behind an authenticating proxy/VPN are not directly exploitable) and that the target encrypted notebook must be unlocked at the time of access.

This is a genuine high-priority confidentiality risk, not merely an inflated CVSS number. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N) describes a network-reachable, low-complexity, unauthenticated attack with no user interaction, and the impact metrics (VC:H, SC:H) reflect complete confidentiality loss including a scope-changing effect on the encrypted subsystem - consistent with the description of full decrypted-content exposure. The 9.2 score is credible given the trivial preconditions. No EPSS score, KEV listing, or public POC was provided, so exploitation probability cannot be quantified and there is no confirmed active exploitation; the value of the target (private/encrypted notes) makes it attractive but exploitation requires the specific condition that an encrypted notebook is currently unlocked and publishing is reachable. Integrity and availability are unaffected (VI:N/VA:N), so this is a read-only disclosure issue.

An attacker who can reach a victim's SiYuan instance over the network browses the publish API and enumerates notebooks, including one that is encrypted but currently unlocked. Without providing credentials or the encryption key, the attacker requests the notebook's documents and receives them in fully decrypted form, harvesting private notes. Given AV:N/AC:L/PR:N/UI:N this requires only HTTP access with no special tooling, though no public POC is currently identified.