New MalDoc in PDF’ Cyberattack Has Been Discovered


JPCERT, Japan’s computer emergency response team, has recently uncovered a new sophisticated ‘MalDoc in PDF’ cyberattack. This attack, detected in July 2023, cleverly evades detection by concealing malicious Word files within PDF documents.  The file analyzed by JPCERT makes use of polyglots to confuse analysis tools and evade detection. While most scanning engines and tools identify it as a PDF, office applications can open it as a standard Word document (.doc). This unique characteristic makes it recognizable to a wide range of software, enabling its versatile usage across different platforms.

What is MalDoc, and how does it work?

MalDoc is a technique employed by attackers to conceal infected Word documents within PDF files. Upon opening the PDF file, the embedded MalDoc triggers the infection process, employing tactics like image overlays to obscure the infected document. This clever camouflage poses challenges for antivirus software detection and user identification. The use of MalDoc in PDF format also enables attackers to evade detection by conventional PDF analysis tools like ‘pdfid’ or other automated tools that only scrape the surface layer of the file. Nonetheless, JPCERT emphasizes that alternative analysis tools such as ‘OLEVBA’ can still detect the malicious content hidden within the polyglot.

maldoc dump view

Why do attackers use MalDoc?

Malicious actors employ MalDoc to evade security measures designed to detect and thwart malware infections. By concealing the infected Word document within a PDF file, they exploit the user’s confidence in the perceived safety of the PDF format, commonly used for sharing documents. Moreover, as PDF files frequently serve as a means to disseminate sensitive information, they become an attractive target for these attackers.

How does MalDoc affect businesses?

MalDoc attacks can inflict significant harm on businesses, leading to data breaches, financial losses, and reputational damage. By exploiting MalDoc, attackers gain unauthorized access to corporate networks, pilfer sensitive data, and propagate malware to interconnected devices.

How can you protect yourself against MalDoc?

As of now MalDoc in PDF does not bypass security settings that disable the automatic execution of macros in Microsoft Office. Therefore, these security measures still provide adequate protection. To disable macros in Microsoft Office apps, users can visit this website and follow the provided instructions. Users also should be wary of emails containing suspicious attachments or links and always question the legitimacy of any file – even if it appears to come from a legitimate source. It is also essential to keep your system up-to-date with the latest security patches.

Businesses should use a multi-layered defense strategy that combines traditional signature detection with other advanced techniques such as behavior monitoring, machine learning, deep learning, and sandboxing. This approach provides an effective solution against MalDoc in PDF and other forms of malicious attacks.

Finally, it is important to educate users and make them aware of the risks associated with suspicious attachments or emails.


In conclusion, MalDoc is a sneaky technique used by attackers to infect devices with malware. They hide infected Word documents inside PDF files, posing a serious threat. To protect your business against MalDoc, it’s important to stay alert and have a solid security strategy in place.

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