CVE-2026-87807 in SiYuan
Summary
by MITRE • 09/09/2026
siyuan versions before v3.8.2 contain an authenticated SQL injection vulnerability in the fullTextSearchBlock endpoint's method=1 query parameter. Attackers can inject UNION SELECT statements to read the entire blocks table, bypassing publish-access controls and exposing all document content and sensitive attributes.
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Analysis
by VulDB Data Team • 09/09/2026
The security flaw identified in Siyuan versions prior to v3.8.2 represents a critical authenticated SQL injection vulnerability located within the fullTextSearchBlock endpoint. This specific weakness is triggered by improper neutralization of special elements used in an SQL command, specifically through the method=1 query parameter. Unlike many vulnerabilities that require unauthenticated access or complex privilege escalation paths, this flaw allows any user with valid authentication credentials to exploit the issue directly. The core technical failure lies in the application's handling of input data where the value provided for the method parameter is incorporated into a database query without adequate sanitization or the use of prepared statements. This lack of proper validation enables an attacker to manipulate the structure of the SQL command executed by the backend system, effectively breaking out of the intended logical flow and injecting arbitrary SQL code.
The operational impact of this vulnerability is severe due to its ability to bypass existing access controls. By leveraging UNION SELECT injection techniques, an authenticated user can construct malicious queries that retrieve data from tables other than the one originally targeted. In this specific instance, the attacker targets the blocks table, which serves as a foundational storage component for Siyuan documents. The exploitation of this flaw allows the extraction of all document content stored within the application's database. This includes not only the textual body of notes and pages but also sensitive metadata attributes associated with each block. Consequently, the confidentiality integrity of user data is completely compromised, as an attacker can exfiltrate private information that was intended to be restricted by publish-access controls or other permission settings implemented at a higher logical layer.
This vulnerability aligns closely with Common Weakness Enumeration category CWE-89, which classifies improper neutralization of special elements used in an SQL command. The exploitation technique described falls under the MITRE ATT&CK framework's T1059 subcategory for Command and Scripting Interpreter techniques, specifically involving database commands to extract data from a backend system. Furthermore, it relates to CWE-284 regarding Improper Access Control, as the successful exploitation allows access to resources that should be restricted by the application's authentication and authorization mechanisms. The ability to bypass publish-access controls highlights a significant design flaw where security decisions based on user permissions are not consistently enforced at the data retrieval layer, allowing lower-level database operations to override higher-level policy restrictions.
Mitigation for this vulnerability requires immediate action from system administrators and developers managing Siyuan instances. The primary remediation step is to upgrade the software environment to version v3.8.2 or later, where the input validation logic has been corrected to properly sanitize inputs passed through the fullTextSearchBlock endpoint. For environments that cannot be immediately upgraded, temporary mitigations should focus on restricting network access to the affected endpoints using web application firewalls or reverse proxy configurations that filter out suspicious SQL injection patterns in query parameters. Additionally, implementing strict parameterized queries for all database interactions involving user-supplied input is essential to prevent similar flaws from being introduced elsewhere in the codebase. Regular security audits and static analysis of the source code can help identify other potential instances where dynamic SQL construction might occur without adequate safeguards against injection attacks.