Summary

Possible Remote Code Execution when performing file upload based on Jakarta Multipart parser.

Who should read this

All Struts 2 developers and users

Impact of vulnerability

Possible RCE when performing file upload based on Jakarta Multipart parser

Maximum security rating

Critical

Recommendation

Upgrade to Struts 2.3.32 or Struts 2.5.10.1

Affected Software

Struts 2.3.5 - Struts 2.3.31, Struts 2.5 - Struts 2.5.10

Reporter

Nike Zheng <nike dot zheng at dbappsecurity dot com dot cn>

CVE Identifier

CVE-2017-5638

Problem

It is possible to perform a RCE attack with a malicious Content-Type value. If the Content-Type value isn't valid an exception is thrown which is then used to display an error message to a user.

Solution

If you are using Jakarta based file upload Multipart parser, upgrade to Apache Struts version 2.3.32 or 2.5.10.1. You can also switch to a different implementation of the Multipart parser.

Backward compatibility

No backward incompatibility issues are expected.

Workaround

Implement a Servlet filter which will validate Content-Type and throw away request with suspicious values not matching multipart/form-data.

Other option is to remove the File Upload Interceptor from the stack, just define your own custom stack and set it as a default - please read How do we configure an Interceptor to be used with every Action. This will work only for Struts 2.5.8 - 2.5.10.

<interceptors>
    <interceptor-stack name="defaultWithoutUpload">
        <interceptor-ref name="exception"/>
        <interceptor-ref name="alias"/>
        <interceptor-ref name="servletConfig"/>
        <interceptor-ref name="i18n"/>
        <interceptor-ref name="prepare"/>
        <interceptor-ref name="chain"/>
        <interceptor-ref name="scopedModelDriven"/>
        <interceptor-ref name="modelDriven"/>
        <interceptor-ref name="checkbox"/>
        <interceptor-ref name="datetime"/>
        <interceptor-ref name="multiselect"/>
        <interceptor-ref name="staticParams"/>
        <interceptor-ref name="actionMappingParams"/>
        <interceptor-ref name="params"/>
        <interceptor-ref name="conversionError"/>
        <interceptor-ref name="validation">
            <param name="excludeMethods">input,back,cancel,browse</param>
        </interceptor-ref>
        <interceptor-ref name="workflow">
            <param name="excludeMethods">input,back,cancel,browse</param>
        </interceptor-ref>
        <interceptor-ref name="debugging"/>
    </interceptor-stack>
</interceptors>
<default-interceptor-ref name="defaultWithoutUpload"/>
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