PDF Malware Protected by AES-256 : Adobe Systems released a security update for Adobe Acrobat and Reader 9.x for Windows on December 16, 2011, in order to fix a zero-day vulnerability. As Vikram Thakur reported recently , there have been zero-day attacks using this PDF vulnerability, dropping Backdoor.Sykipot on to the compromised computer. We have found another variant of PDF malware in the wild using the same vulnerability. This version of PDF malware uses an encryption method that is found natively in the PDF specifications. As I wrote in my Portable Document Format Malware whitepaper , the encryption method used by PDF malware has changed from RC4 to AES. The AES specifies the encryption key has 128 bits in length. However, this variant adopts AES-256 as the encryption method, with a key length of 256 bits. The specification for the encryption method using AES-256 in a PDF is described as an extension of the ISO32000 version of PDF specification. It is able to download the PDF ex...
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