This indicates an attack attempt to exploit an Information Disclosure vulnerability in Microsoft Browsers.
This vulnerability is due to an error when the affected application handles maliciously crafted HTTP file. A remote attacker may be able to exploit this to gain access to sensitive information, via a crafted HTTP file.
Internet Explorer 9
Internet Explorer 10
Internet Explorer 11
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.