MVEL is an expression language engine designed to compile and execute code provided by trusted expression authors. MVEL expressions are functionally equivalent to Java code and have the same capabilities, including file system access, network access, and arbitrary code execution.

This is by design. Like other expression language engines (MVEL2, Apache Commons JEXL, Groovy, Spring Expression Language), MVEL compiles and executes code. Some of these projects offer optional sandboxing (e.g., JEXL's JexlSandbox, SpEL's SimpleEvaluationContext), but none guarantee safe execution of untrusted input.

Threat model: MVEL assumes all expression authors are trusted. Executing untrusted expressions is not a supported use case.

If you embed MVEL in your application:

• Never pass untrusted user input directly to the MVEL compiler (for example, via new MVELCompiler().compile(...), new MVEL().compile(...), or any other compilation entry point).
• The responsibility for restricting who can author expressions lies with your application, not with MVEL.
• Treat MVEL expressions with the same level of trust as Java source code.
• If untrusted input must be processed, validate and sanitize it before it reaches any MVEL compilation entry point, or run MVEL in an isolated environment (e.g., a sandboxed JVM or container).

We consider the following to be valid security reports:

• Bugs that allow bypassing a configured security mechanism (e.g., a class allowlist/blocklist, if such a feature is implemented)
• Vulnerabilities in MVEL's build or distribution infrastructure
• Bugs that cause MVEL to behave contrary to its documented security model

The following are not considered vulnerabilities, as they reflect intended functionality:

• Ability to execute arbitrary code via MVEL expressions
• Access to JDK APIs (file I/O, networking, reflection) from expressions
• Remote code execution when untrusted input is passed to the compiler without sanitization by the consuming application

If you discover a security vulnerability in MVEL, please report it through GitHub's private vulnerability reporting:

1. Go to the Security Advisories page
2. Fill in the details and submit

This ensures the report is handled privately and responsibly. Please do not open a public GitHub issue for security vulnerabilities.

Accepted vulnerabilities will be disclosed via GitHub Security Advisories. We will coordinate disclosure timing with the reporter. Reporters will be credited unless they request anonymity.

MVEL3 is currently in alpha (3.0.0-SNAPSHOT) and has not had a stable release. Security reports are still welcome and will be evaluated on a case-by-case basis.

Once stable releases are published, this section will list which versions receive security fixes. During the alpha phase, only the main branch HEAD is considered supported.