CVE-2023-30331: 
Java vulnerability analysis and mitigation

A server-side template injection (SSTI) vulnerability was discovered in Beetl version 3.15.0, identified as CVE-2023-30331. The vulnerability exists in the render function of the template engine, allowing attackers to execute arbitrary code via crafted payloads. The vulnerability was disclosed on May 3, 2023, affecting Beetl template engine version 3.15.0 (NVD).

The vulnerability stems from the template engine's security manager implementation which uses a blacklist-based approach for restricting dangerous operations. The DefaultNativeSecurityManager class attempts to block access to dangerous Java classes like Runtime, Process, ProcessBuilder, and System, but can be bypassed using Java reflection. The vulnerability has received a CVSS v3.1 base score of 9.8 (CRITICAL) with vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (NVD, Gitee Issue).

The vulnerability allows attackers to execute arbitrary code on the server through template injection. By bypassing the security restrictions, an attacker can perform various malicious actions including command execution, file operations, and network requests. This gives attackers potential full control over the affected server (Gitee Issue).

The recommended mitigation is to restrict the use of Java reflection in templates. The vendor has updated the security manager to add Class to the blacklist of restricted classes. Additional security measures include blocking access to the sun package, java.io, and java.net packages. For applications using Beetl, it's recommended to disable native Java calls when not required (Gitee Issue).