Yamcs is a mission control framework. Prior to 5.12.7, the Yamcs script evaluation engine for Python algorithms dynamically compiled and evaluated user-controlled algorithm text using Jython through the JSR-223 ScriptEngine API without enforcing a secure sandbox, so an authenticated user with the ChangeMissionDatabase privilege could override an existing Python algorithm's logic through the mission database REST API and import and execute arbitrary Java classes such as java.lang.Runtime to achieve remote code execution on the underlying host operating system. This issue is fixed in versions 5.12.7 and 5.13.0, which disable algorithm editing by default.

Affected: Maven: org.yamcs:yamcs-core

### Summary A Server-Side Code Injection vulnerability exists in the Yamcs script evaluation engine for Python algorithms. The application dynamically compiles and evaluates user-controlled algorithm text using Jython (via the JSR-223 ScriptEngine API) without enforcing a secure sandbox. An authenticated user with the `ChangeMissionDatabase` privilege can exploit this by overriding the algorithm logic through the REST API, achieving Remote Code Execution (RCE) on the underlying host operating system.

### Details The vulnerability lies in how Yamcs handles dynamic script evaluation. When a user updates an algorithm via the MDB (Mission Database) API (`/api/mdb/{instance}/realtime/algorithms/{name}`), the `AlgorithmManager` uses the `ScriptAlgorithmExecutorFactory` to instantiate a JSR-223 `ScriptEngine` (in this case, Jython/Python).

Because Jython allows seamless interoperability with native Java classes, an attacker can import and execute arbitrary Java classes such as `java.lang.Runtime`. Any valid Python algorithm can be overwritten with a malicious payload that executes OS-level commands.

### PoC

**Prerequisites:** 1. A running Yamcs instance with the Jython engine available in its classpath (e.g., `jython-standalone` dependency included). 2. An active authentication token for a user with the `SystemPrivilege.ChangeMissionDatabase` privilege. 3. An existing algorithm defined in the Mission Database (MDB) with its language explicitly set to `python` (e.g., a custom `…