The vulnerability resides in SiYuan’s /api/network/forwardProxy endpoint, which accepts a user‑controlled URL and forwards arbitrary HTTP requests from the server. Because the endpoint performs no validation, authenticated users can instruct the server to reach any address, including internal networks, localhost, or cloud metadata services, and retrieve the complete response body and headers. This enables the attacker to read sensitive internal resources or metadata, potentially exfiltrating confidential data or compromising internal systems. The weakness is categorized as CWE‑918 – Server‑Side Request Forgery.

Affected products include SiYuan, a personal knowledge management system. All releases prior to version 3.6.0 are vulnerable; versions 3.6.0 and later incorporate a fix that validates the target URL and restricts outbound access.

The issue carries a CVSS score of 8.3 (High) and an EPSS probability of less than 1 %, indicating a lower likelihood of arbitrary exploitation but a severe impact if exploited. The vulnerability is not listed in CISA’s KEV catalog. The likely attack vector requires an authenticated user; thus, compromised credentials or social‑engineering to gain access to the application are prerequisites. Once authenticated, an attacker can direct the server to access arbitrary endpoints, creating a potential data breach or further internal compromise.