Cybersecurity researchers have turned their attention to a new phishing campaign that uses corrupted Microsoft Office documents and ZIP archives as a way to bypass email protection.
“Ongoing attack evades antivirus software, prevents sandboxing and bypasses Outlook’s spam filters, allowing malicious emails to reach your inbox”, ANY.RUN said in a series of posts on X.
Malicious activity involves sending emails containing ZIP archives or Office attachments that are intentionally corrupted in a way that cannot be scanned by security tools. These messages are designed to trick users into opening attachments with false promises of employee benefits and bonuses.
In other words, the damaged state of the files means that they are not flagged by email filters and antivirus software as suspicious or malicious.
However, the attack still works because it takes advantage of the built-in recovery mechanisms of programs such as Word, Outlook, and WinRAR to restart such damaged files in recovery mode.
ANY.RUN revealed that this attack technique has been used by threat actors since at least August 2024, describing it as a potential zero-day used to avoid detection.
The ultimate goal of these attacks is to trick users into opening mined documents that embed QR codes that, when scanned, redirect victims to rogue websites to deploy malware or fake login pages to steal credentials.
The data once again illustrates how attackers are constantly looking for previously unseen methods to bypass email security software and ensure that their phishing emails reach victims’ mailboxes.
“Although these files are successfully running in the OS, they remain undetected by most security solutions due to the lack of proper procedures for their file types,” said ANY.RUN.
“The file remains undetectable by security tools, but user applications process it seamlessly thanks to built-in recovery mechanisms that attackers use.”
