CVE-2026-18737 in Shlink
Summary
by MITRE • 08/04/2026
Shlink contains a blind SQL injection vulnerability that allows any authenticated API key holder to inject arbitrary SQL fragments by supplying an unvalidated direction value in the orderBy query parameter of the tag statistics endpoint. Attackers can craft a malicious direction string containing SQL subqueries that flows unsanitized into a Doctrine QueryBuilder ORDER BY clause, enabling time-based, boolean-oracle, and error-based extraction of sensitive data including long URLs, visitor records, IP addresses, geolocation data, user agents, and hashed API key secrets from any tenant.
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Analysis
by VulDB Data Team • 08/04/2026
This vulnerability exists within the Shlink web application's tag statistics endpoint where improper input validation allows authenticated users to manipulate database queries through the orderBy parameter. The flaw manifests when an attacker supplies a malicious direction value that bypasses sanitization checks and directly influences the Doctrine QueryBuilder ORDER BY clause. This represents a classic blind sql injection vulnerability that operates without direct output feedback, relying instead on timing delays, boolean responses, or error messages to extract information from the underlying database.
The technical implementation of this vulnerability leverages the application's failure to properly validate user-supplied input before incorporating it into database queries. When an authenticated API key holder makes a request to the tag statistics endpoint with a crafted direction parameter, the system fails to sanitize the input before passing it to the QueryBuilder component. This allows attackers to inject SQL fragments that execute within the context of the database connection, creating opportunities for data exfiltration and unauthorized access to sensitive tenant information.
The operational impact of this vulnerability extends beyond simple data theft to encompass complete compromise of tenant privacy and application integrity. Attackers can exploit this weakness to extract long URLs, visitor records, IP addresses, geolocation data, user agent strings, and hashed API key secrets from any tenant within the system. The time-based blind injection techniques enable attackers to infer database contents through timing variations, while boolean or error-based approaches provide more direct methods for data extraction. This vulnerability essentially provides attackers with a backdoor into the application's data layer without requiring additional authentication mechanisms.
Organizations using Shlink should immediately implement input validation controls that sanitize all user-supplied parameters before processing them in database queries. The fix requires implementing proper parameter binding or escaping techniques to prevent injection attacks, along with comprehensive input validation for all query parameters including orderBy values. Security controls should include rate limiting on API endpoints, monitoring for unusual query patterns, and regular security testing of database interactions. This vulnerability aligns with CWE-89 which addresses improper neutralization of special elements used in SQL commands, and maps to ATT&CK technique T1213.002 for data from information repositories. Organizations should also consider implementing web application firewalls and database activity monitoring solutions to detect and prevent exploitation attempts.