Home > Security Bulletins > S2-020


Upgrade Commons FileUpload to version 1.3.1 (avoids DoS attacks) and adds 'class' to exclude params in ParametersInterceptor (avoid ClassLoader manipulation)

Who should read this

All Struts 2 developers and users

Impact of vulnerability

DoS attacks and ClassLoader manipulation

Maximum security rating



Developers should immediately upgrade to Struts

Affected Software

Struts 2.0.0 - Struts 2.3.16


Peter Magnusson (peter.magnusson at omegapoint.se), Przemysław Celej (p-celej at o2.pl)

CVE Identifier

CVE-2014-0050 (DoS), CVE-2014-0094 (ClassLoader manipulation)


The default upload mechanism in Apache Struts 2 is based on Commons FileUpload version 1.3 which is vulnerable and allows DoS attacks. Additional ParametersInterceptor allows access to 'class' parameter which is directly mapped to getClass() method and allows ClassLoader manipulation.


In Struts, Commons FileUpload was updated to version 1.3.1 and "class" was added to excludeParams in struts-default.xml configuration of ParametersInterceptor.

Backward compatibility

No backward compatibility problems are expected.


If you cannot upgrade to version which is strongly advised, you can apply below workarounds:

Upgrade commons-fileupload

The fixed commons-fileupload library is a drop-in replacement for the vulnerable version. Deployed applications can be hardened by replacing the commons-fileupload jar file in WEB-INF/lib with the updated jar. For Maven
based Struts 2 projects, the following dependency needs to be added:


Exclude 'class' parameter

Simple add '^class\.*' to the list of excludeParams as below

<interceptor-ref name="params">
  <param name="excludeParams">^class\..*,^dojo\..*,^struts\..*,^session\..*,^request\..*,^application\..*,^servlet(Request|Response)\..*,^parameters\..*,^action:.*,^method:.*</param>