CVE-2020-13936

What it actually does

Modification of Velocity templates enables execution of arbitrary Java code or system commands with privileges of the servlet container account.

Why it matters to the business

Successful exploitation can result in complete server takeover, unauthorized data access, service disruption, and lateral movement within the environment.

How an attack unfolds

An attacker with permission to upload or edit templates creates a malicious Velocity template containing code execution directives; when the application processes the template, the engine evaluates the directives and runs the embedded commands.

How to fix it

Upgrade Apache Velocity Engine to a version beyond 2.2. Restrict untrusted users from uploading or modifying templates and enforce strict access controls on template handling.

How to confirm the fix worked

Verify the deployed Velocity Engine version is newer than 2.2. Audit code paths that accept user-supplied templates and confirm privilege restrictions are enforced.

Typical attack path

1. Locate applications using vulnerable Apache Velocity Engine versions
2. Obtain ability to upload or modify templates through application features
3. Craft and submit a template embedding arbitrary Java or command execution payloads
4. Trigger template rendering to activate the payload and execute commands

How to detect it

Search application and server logs for unexpected template uploads or modifications followed by anomalous process spawns or command executions; review audit trails for template rendering events originating from untrusted sources.

What your security team should do

• Prioritize upgrade of all Velocity Engine instances to a fixed version
• Review and restrict template modification permissions across applications
• Implement additional input validation and sandboxing around template processing
• Monitor EPSS score and emerging exploit maturity for increased urgency