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Apache Struts 2 Documentation
S2-020
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## Summary

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 | Important
Recommendation | Developers should immediately upgrade to Struts 2.3.16.1
Affected Software | Struts 2.0.0 - Struts 2.3.16
Reporter | Mark Thomas (markt at apache.org),Przemysław Celej (p-celej at o2.pl)
CVE Identifier |

## Problem

Default upload mechanism in Apache Struts 2 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.

## Solution

In Struts 2.3.16.1, Commons FileUpload was updated to version 1.3.1 and "class" was added to excludeParams in struts-defaul.xml configuration of ParametersInterceptor.