Encrypted VelvetSweatshop Password Still a Threat to Excel Files
Office documents, such as Word and Excel files, can be password-protected using a symmetric key encryption mechanism involving one password which is the key to both encrypt and decrypt a file. Malware writers use this key as an additional evasion technique to hide malicious code from anti-virus (AV) scanning engines. The problem is that encrypting a file introduces the disadvantage of requiring a potential victim to enter a password (which is normally included in the phishing or spam email containing the encrypted attachment). This makes the email and the attachment very suspicious, thus greatly reducing the chance that the intended victim will open the encrypted malicious attachment.
The good news (for the attackers) is that Microsoft Excel can automatically decrypt a given encrypted spreadsheet without asking for a password if the password for encryption happens to be VelvetSweatshop. This is a default key stored in Microsoft Excel program code for decryption. It’s a neat trick that attackers can leverage to encrypt malicious Excel files in order to evade static-analysis-based detection systems, while eliminating the need for a potential victim to enter a password.
The embedded VelvetSweatshop key in Excel is not a secret. It has been widely reported for many Continue reading
