What the vulnerability does
01Description
OGNL is an Object Graph Navigation Library for Java. Prior to 3.4.13, the optional stricter-invocation mode in OgnlRuntime.invokeMethod checks the declaring class of the method that OGNL invokes but does not block java.lang.reflect.Method, java.lang.reflect.Constructor, or java.lang.reflect.Field. An attacker-controlled expression can invoke one of these reflection objects as a proxy for a method on a blocked class, causing the real operation to execute inside JDK reflection without passing through the stricter-invocation check again. Exploitation requires an application to evaluate untrusted OGNL expressions, use the default or an equivalently permissive MemberAccess that permits reflection, and rely on stricter invocation as a sandbox. Applications using a restrictive MemberAccess, including Apache Struts with SecurityMemberAccess, are not affected by this bypass. This issue is fixed in 3.4.13.
