Episode 38: Image, File, and Voice-Based Threats (Domain 2)

While emails and text messages are well-known vectors, attackers also exploit images, file attachments, and voice communication to bypass traditional security controls. In this episode, we explore steganography—embedding malicious code or data within image files—as well as the risks posed by file-based threats hidden in PDFs, Office documents, and ZIP archives that exploit unpatched applications or social engineering weaknesses. We also examine voice-based phishing, or vishing, where attackers impersonate trusted parties over the phone to trick targets into revealing sensitive information, transferring funds, or installing remote access tools. These methods often escape automated detection because they rely on human interaction or use file formats that appear harmless. Defending against them requires a combination of endpoint protection, application whitelisting, call-back verification policies, and strong user education. As attackers diversify their methods, defenders must account for all input channels—not just the obvious ones.

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In this episode, we are exploring three threat vectors that often fly under the radar but can have serious consequences: image-based attacks, file-based threats, and voice call scams known as vishing. Each of these methods uses familiar formats to deliver malicious payloads or manipulate victims. Understanding how they work and how to recognize the warning signs is key to stopping these threats before they cause damage.
Let’s begin with image-based attacks. Images are typically seen as harmless, especially when shared in casual or professional settings. But attackers can embed malicious content inside image files using techniques like steganography or by modifying metadata. Steganography is the practice of hiding data within other files—such as inserting code into the pixels of a picture or hiding commands in the image’s metadata fields.
One of the challenges with image-based attacks is that they are difficult to detect with traditional scanning tools. The image appears normal to the human eye, and unless a system is specifically configured to look for hidden content, the threat may go unnoticed. Attackers can use these techniques to deliver malware, exfiltrate data, or send instructions to compromised systems.
For example, in one documented case, an attacker embedded command and control instructions within a photo uploaded to a website. Malware on infected machines downloaded the image and interpreted the hidden instructions, allowing the attacker to remotely control the devices without raising suspicion.
To reduce the risk of image-based attacks, organizations should monitor image uploads and downloads, limit the types of image files that can be processed by sensitive applications, and use advanced malware detection tools that analyze file behavior rather than just file type.
Now let’s turn to file-based threats. This category includes malicious documents, scripts, and executables that are delivered through common file formats like PDF, Word documents, Excel spreadsheets, or application installers. These files may contain embedded macros, scripts, or exploits that take advantage of vulnerabilities in the software used to open them.
For instance, an attacker might send an email with a seemingly legitimate invoice attached as a Word document. When the victim opens the file and enables macros, a hidden script executes and installs malware. These types of attacks are common in phishing campaigns and are often used to deliver ransomware, keyloggers, or remote access tools.
Executable files—such as those ending in dot E X E—are also dangerous if downloaded from untrusted sources. Attackers may disguise malicious applications as legitimate software installers. When a user runs the file, the malware installs itself silently and begins stealing data or spreading across the network.
Safe handling practices are critical in defending against file-based threats. Users should be trained never to open unexpected attachments or enable macros in documents. File downloads should be restricted to trusted sites, and endpoint protection systems should scan all downloaded and opened files for malicious content. Application whitelisting and sandboxing can also help prevent suspicious files from executing or affecting other parts of the system.
Finally, let’s talk about voice call threats, commonly known as vishing. Vishing is a form of phishing that takes place over the phone. Attackers use social engineering techniques to trick victims into revealing sensitive information, installing software, or making unauthorized payments.
The effectiveness of vishing lies in its personal and urgent nature. Attackers may impersonate tech support agents, bank representatives, or even government officials. They often use caller ID spoofing to make the call appear legitimate. During the call, they use psychological tactics such as fear, urgency, or authority to pressure the victim into taking immediate action.
For example, a victim might receive a call from someone claiming to be from their credit card provider, saying there has been suspicious activity and asking the victim to verify their full account number. In other cases, attackers claim to be from the I T department and ask for remote access to resolve a fake problem.
Vishing attacks have been used to target both individuals and organizations. In one case, an attacker impersonated a company executive and called the finance department, requesting an urgent wire transfer. The employee followed the instructions, and the money was sent before the scam was discovered.
Preventing vishing starts with awareness. Employees should be trained to verify calls independently—never providing information or access unless the request is confirmed through known, official channels. Organizations should implement clear policies for handling sensitive information over the phone, including requiring callbacks using verified numbers and escalating suspicious calls to supervisors or security teams.
As you prepare for the Security Plus exam, remember that not all cyberattacks come in the form of obvious code or brute-force hacking. Some are hidden in image files. Others are disguised as harmless documents. And some are delivered by voice, using manipulation instead of malware. You may be asked to identify the type of threat vector described in a scenario or to recommend prevention techniques. Pay close attention to clues like file types, behavior patterns, and user interaction—these details often reveal the underlying vector at play.