This indicates an attack attempt to exploit a Security Bypass vulnerability in Apache Struts.
The vulnerability is caused by an error in MultiPageValidator when handles requests with malicious page parameter. A remote attacker may be able to exploit this to bypass access restrictions via a crafted HTTP request.
Struts 1.x through 1.3.10
Security Bypass: Remote attackers can bypass security checking of vulnerable systems.
Apply patch, available from the web site.