CVE-2025-68948: 
NixOS vulnerability analysis and mitigation

CVE-2025-68948 is an information disclosure and authentication bypass vulnerability in SiYuan Note, a self-hosted open-source personal knowledge management application. The vulnerability stems from the use of a hardcoded cryptographic secret in the session store, rendering session cookie encryption ineffective. It affects SiYuan versions 3.5.1 and earlier, with version 3.5.2 containing the fix. The vulnerability was published on December 26–27, 2025, and carries a CVSS v3.1 base score of 8.1 (High) (GitHub Advisory, Red Hat CVE).

The root cause is classified as CWE-321 (Use of Hard-coded Cryptographic Key) and CWE-798 (Use of Hard-coded Credentials). The vulnerable component is the initSession function in kernel/server/serve.go, where the application initializes the cookie store using a static string hardcoded in the source code as the encryption and signing key. Because the key is publicly visible in the GitHub repository, any attacker who obtains a user's session cookie can decrypt it locally using the known key to extract the AccessAuthCode — the user's primary authentication credential. A public proof-of-concept script demonstrating the decryption process is available at https://gist.github.com/28Hus/1dfc3e2abaf9b099686c992296a89c8f (GitHub Advisory).

Successful exploitation allows an attacker to decrypt intercepted session cookies and recover the AccessAuthCode in plaintext, enabling full account takeover of the SiYuan instance. Unlike standard session hijacking (which is limited by session expiry), possession of the AccessAuthCode allows the attacker to generate new valid sessions indefinitely, granting persistent administrative access to private notes and potentially the underlying server. The confidentiality, integrity, and availability of the knowledge management system are all at risk (GitHub Advisory).

A public proof-of-concept script is available on GitHub Gist, demonstrating cookie decryption using the hardcoded key. There is no current evidence of in-the-wild exploitation, and no threat actor attribution has been reported. The vulnerability is not listed in the CISA KEV catalog. The EPSS score is approximately 0.023% (very low probability of near-term exploitation), though the availability of a working PoC lowers the barrier for exploitation (GitHub Advisory, Feedly).

1. Reconnaissance: Identify internet-facing or LAN-accessible SiYuan Note instances running version 3.5.1 or earlier, using network scanning tools or Shodan.
2. Session Cookie Interception: Obtain the victim's session cookie via network interception on unencrypted HTTP connections (e.g., LAN sniffing with Wireshark), cross-site scripting, or other client-side attack vectors.
3. Locate Hardcoded Key: Retrieve the static encryption/signing key from the publicly available SiYuan source code in kernel/server/serve.go (the initSession function).
4. Decrypt the Cookie: Run the public PoC script (https://gist.github.com/28Hus/1dfc3e2abaf9b099686c992296a89c8f) with the intercepted cookie value as input, using the hardcoded key to decrypt the session payload.
5. Extract AccessAuthCode: The script outputs the plaintext AccessAuthCode from the decrypted session.
6. Authenticate and Take Over: Use the recovered AccessAuthCode to authenticate directly to the SiYuan instance, gaining full administrative control and persistent access to private notes and server resources (GitHub Advisory).

• Network: Unusual or repeated authentication requests to a SiYuan instance from unexpected IP addresses or geographic locations; unencrypted HTTP traffic containing session cookies on local networks.
• Logs: SiYuan access logs showing successful authentication events from IP addresses not associated with the legitimate user; multiple session creations using the same AccessAuthCode from different clients.
• Process/Application: Unexpected administrative actions within SiYuan (e.g., note access, export, or configuration changes) not initiated by the legitimate user.
• File System: Unexpected exports or downloads of note data from the SiYuan data directory.

Users should immediately upgrade SiYuan to version 3.5.2 or later, which contains the fix for this vulnerability. If immediate patching is not possible, restrict network access to SiYuan instances (e.g., bind to localhost or use a VPN/firewall) to prevent session cookie interception, and ensure HTTPS is enforced to protect cookies in transit. Review authentication logs for suspicious activity during the period the vulnerable version was in use (GitHub Advisory).

The vulnerability was reported by security researcher 28Hus and disclosed via GitHub's security advisory program. A technical write-up was published at https://infinitsec.net/posts/cve-2025-68948-siyuan-information-disclosure-and-authentication-bypass-via-hardcoded-session-s, providing additional context on the issue. The vulnerability received coverage from automated CVE tracking services and security aggregators, but no major vendor statements or widespread community debate have been noted beyond the initial advisory.