Apache Struts2 ParametersInterceptor Remote Command Execution

The OGNL extensive expression evaluation capability in XWork in Struts 2.0.0 through 2.1.8.1, as used in Atlassian Fisheye, Crucible, and possibly other products, uses a permissive whitelist, which allows remote attackers to modify server-side context objects and bypass the "#" protection mechanism in ParameterInterceptors via the (1) #context, (2) #_memberAccess, (3) #root, (4) #this, (5) #_typeResolver, (6) #_classResolver, (7) #_traceEvaluations, (8) #_lastEvaluation, (9) #_keepLastEvaluation, and possibly other OGNL context variables, a different vulnerability than CVE-2008-6504.