A critical vulnerability (CVE-2026-63233) was identified in Koollab LMS involving SQL injection and unsafe deserialization. An authenticated attacker can exploit the assessment overall answer endpoint to inject malicious SQL and control data passed to PHP's unserialize() function. This allows the attacker to write a webshell to a publicly accessible server location. Once the webshell is in place, arbitrary code execution on the server becomes possible. The vulnerability chain combines two serious weaknesses: SQL injection and insecure deserialization. The issue was reported via NVD (NIST) and also flagged by the Cyber Security Agency of Singapore (CSA). The attack requires authentication, but the resulting impact is severe, enabling full server compromise. Organizations using Koollab LMS should apply patches or mitigations immediately.