Summary
XWork ParameterInterceptors bypass allows OGNL statement execution
Who should read this |
All Struts 2 developers |
---|---|
Impact of vulnerability |
Remote server context manipulation |
Maximum security rating |
Critical |
Recommendation |
Developers should immediately upgrade to Struts 2.0.11.2 or upgrade to XWork 2.0.5 |
Affected Software |
Struts 2.0.0 - Struts 2.0.11.1 |
Original JIRA Ticket |
|
Reporter |
Meder Kydyraliev, Google Security Team |
Problem
OGNL provides, among other features, extensive expression evaluation capabilities (http://www.ognl.org/2.6.9/Documentation/html/LanguageGuide/expressionEvaluation.html). The vulnerability allows a malicious user to bypass the '#'-usage protection built into the ParametersInterceptor, thus being able to manipulate server side context objects.
So, for instance, to set #session.user to '0wn3d' the following parameter name can be used:
('\u0023' + 'session\'user\'')(unused)=0wn3d
which will look as follows once URL encoded:
('\u0023'%20%2b%20'session\'user\'')(unused)=0wn3d
Solution
As of XWork 2.0.5, the ParameterInterceptor was changed to provide a whitelist mechanism for acceptable, non malicious parameter names. Therefore, in the example above, the given parameter will be ignored. You can either obtain a copy of the released XWork 2.0.5 jar as a drop in replacement for the XWork 2.0.4 jar used in Struts 2.0.9 and above, or download a full release of Struts 2.0.11.2, which contains the corrected XWork library.