[Security] Theme template SpEL injection leads to RCE

Prerequisites

• I have searched for related issues in the issues list.
• This is an issue with the Halo project itself. If it is not an issue with the project itself(For example: Installation and deployment issues.), it is recommended to submit it in the Discussions.
• I have tried disabling all plugins to rule out plugins as the cause of the problem.
• If it is an issue with plugins and themes, please submit it in the respective plugin and theme repositories.

System information

部署方式: java -jar halo-2.26.0.jar 数据库: PostgreSQL 17 (Docker, postgres:17-alpine) 操作系统: Ubuntu 24.04 LTS (aarch64) Java: OpenJDK 21 (21.0.11) 端口: 8090（另在 18090 验证）

What is the project operation method?

Source Code

What happened?

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Reproduce Steps

No response

Relevant log output

Additional information

No response