Microsoft Excel Users Warned: Phishing Campaign Spreads Fileless Remcos Malware

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In a landscape where phishing attacks are as prevalent as coffee breaks, Microsoft Excel users are now on high alert due to a recently discovered phishing campaign that's spreading a dangerous fileless malware variant known as Remcos. This clever scheme, brought to our attention by Fortinet's Fortiguard Labs, cleverly employs the vulnerabilities of Microsoft 365 to infiltrate systems, and it’s a wake-up call for anyone who regularly utilizes this staple of office productivity.

The Attack Unraveled: How It Works​

The phishing campaign cleverly masquerades as a benign shipping purchase order, attaching a seemingly innocuous Excel spreadsheet that, once opened, unleashes a whole new world of trouble. By exploiting a known remote code execution vulnerability (CVE-2017-0199), once the user opens this malicious spreadsheet, an HTML application downloads automatically. But it doesn’t stop there; this application acts like a gateway to installing the Remcos malware on the affected machine.
So why is this particular variant of Remcos so concerning? Unlike traditional malware, the Remcos remote access Trojan (RAT) operates entirely in the infected system's memory. This means it leaves no trace on the hard drive, effectively eluding many antivirus and antimalware tools that rely on file signatures to detect malicious software. By operating in the shadows, the malware can engage in activities like screen recording and keylogging without raising alarm bells—a clear demonstration of how cyber threat actors adapt to avoid detection.

Dark Features of Remcos​

As a remote access Trojan, Remcos is akin to a digital locksmith, granting its operator complete access to an unsuspecting user’s computer. It opens the door to:
  • Keylogging: Tracking every keystroke, effectively allowing hackers to obtain sensitive credentials or personal information.
  • Screen Recording: Capturing what's happening on the victim's screen, providing a goldmine of data.
  • Audio Capturing: Some variants can even record audio through a victim's device microphone.
The data harvested is encrypted and relayed to the attackers, who can then exploit this information for various malicious purposes, from identity theft to corporate espionage.

Stay Safe: What You Can Do​

While the specific versions of Microsoft Excel that are vulnerable haven't been clearly identified, it's critical for users to take proactive steps:
  1. Update Microsoft 365 Regularly: Ensure you are using the latest version of Microsoft Office 365. Keeping your software up to date is one of the simplest yet most effective defenses against security vulnerabilities.
  2. Operating System Updates: Keeping your operating system current mitigates risks associated with known vulnerabilities.
  3. Be Wary of Attachments: Approach unexpected emails with attachments, especially those that appear to be invoices or purchase orders, with caution. Verify the source before opening any document.
  4. Utilize Security Software: While traditional antivirus may struggle with fileless malware, consider utilizing comprehensive security solutions that specifically aim to detect abnormal behavior on systems rather than relying solely on infection signatures.
  5. Educate Yourself and Others: Training sessions or informational sheets can help raise awareness about phishing threats in the workplace. The more vigilant everyone is, the harder it becomes for attackers to succeed.

The Bigger Picture: A Continuous Arms Race​

As sophisticated as some attacks may be, they also illuminate larger trends in cybersecurity. The increasing prevalence of fileless malware reveals a broader strategy among cybercriminals: to create malware that is inherently more difficult to detect. This aligns with the growing use of automation and artificial intelligence by attackers, underscoring the constant need for vigilance within the cybersecurity landscape.
Cyber defenders in the corporate arena must continuously innovate their methods and tools to counter these evolving threats. In the battle between attackers and defenders, staying ahead of the game requires not just effective tools, but also an informed and aware user base.
In summary, as attackers become more cunning, your defense should evolve too. By implementing best practices and remaining vigilant, we can all contribute to a safer digital environment. Have you recently updated your Microsoft 365? Share your experiences and strategies for staying safe from phishing attacks in the comments below!

Source: MakeUseOf This Crafty Excel Phishing Campaign Is Spreading Dangerous Fileless Malware