This indicates an attack attempt to exploit a Security Bypass vulnerability in Trustwave ModSecurity.
The vulnerability is due to improper validation of user supplied data when vulnerable module handles a malicious HTTP request. A remote attacker may be able to exploit this to bypass web application firewall and execute arbitrary code via a crafted HTTP request.
Trustwave: SpiderLabs ModSecurity prior to 2.7.6
Security Bypass: Remote attackers can bypass security checks of vulnerable systems.
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