Summary

A server-side template injection was identified in the self-validating (@SelfValidating) feature of dropwizard-validation enabling attackers to inject arbitrary Java EL expressions, leading to Remote Code Execution (RCE) vulnerability.

If you're using a self-validating bean (via @SelfValidating), an upgrade to Dropwizard 1.3.21/2.0.3 or later is strongly recommended.

The changes introduced in Dropwizard 1.3.19 and 2.0.2 (see GHSA-3mcp-9wr4-cjqf/CVE-2020-5245) unfortunately didn't fix the underlying issue completely.

Impact

This issue may allow Remote Code Execution (RCE), allowing to run arbitrary code on the host system (with the privileges of the Dropwizard service account privileges) by injecting arbitrary Java Expression Language (EL) expressions when using the self-validating feature (@SelfValidating, @SelfValidation) in dropwizard-validation.

Patches

The issue has been fixed in dropwizard-validation 1.3.21 and 2.0.3 or later. We strongly recommend upgrading to one of these versions.

The evaluation of EL expressions has been disabled by default now.

In order to use some interpolation in the violation messages added to ViolationCollector, it has to be explicitly allowed by setting SelfValidating#escapeExpressions() to false.

It is also recommended to use the addViolation methods supporting message parameters instead of EL expressions introduced in Dropwizard 1.3.21 and 2.0.3:

• ViolationCollector#addViolation(String, Map<String, Object>
• ViolationCollector#addViolation(String, String, Map<String, Object>
• ViolationCollector#addViolation(String, String, Integer, Map<String, Object>
• ViolationCollector#addViolation(String, String, String, Map<String, Object>

Workarounds

If you are not able to upgrade to one of the aforementioned versions of dropwizard-validation but still want to use the @SelfValidating feature, make sure to properly sanitize any message you're adding to the ViolationCollector in the method annotated with @SelfValidation.

Example:

@SelfValidation
public void validateFullName(ViolationCollector col) {
    if (fullName.contains("_")) {
        // Sanitize fullName variable by escaping relevant characters such as "$"
        col.addViolation("Full name contains invalid characters:  " + sanitizeJavaEl(fullName));
    }
}

See also:
https://github.com/dropwizard/dropwizard/blob/v2.0.3/dropwizard-validation/src/main/java/io/dropwizard/validation/InterpolationHelper.java

References

• GHSA-3mcp-9wr4-cjqf
• #3208
• #3209
• https://docs.jboss.org/hibernate/validator/6.1/reference/en-US/html_single/#section-hibernateconstraintvalidatorcontext

For more information

If you have any questions or comments about this advisory:

• Open an issue in dropwizard/dropwizard
• Start a discussion on the dropwizard-dev mailing list

Security contact

If you want to responsibly disclose a security issue in Dropwizard or one of its official modules, please contact us via the published channels in our security policy:

https://github.com/dropwizard/dropwizard/security/policy#reporting-a-vulnerability