Cyber attackers are capitalizing on an old Microsoft Office vulnerability, specifically targeting Microsoft Excel, to spread the Agent Tesla malware through phishing campaigns. The attackers employ decoy Excel documents attached to invoice-themed emails to trick individuals into opening them. By leveraging the CVE-2017-11882 vulnerability, which is a memory corruption flaw in Microsoft Office’s Equation Editor, the attackers gain the ability to execute code with the user’s privileges.
The infection chain begins with the distribution of Excel documents in phishing emails, prompting recipients to open the attachments. Once the malicious document is opened, it exploits the CVE-2017-11882 vulnerability, allowing the attackers to execute code on the victim’s machine. This vulnerability has been known and exploited for several years, highlighting the importance of keeping software up-to-date and addressing known security flaws promptly.
Zscaler ThreatLabz researchers discovered this recent campaign, shedding light on the attackers’ tactics. After successful exploitation, the malware initiates communication with a malicious destination, leading to the download of additional files without requiring further interaction from the user. The attack utilizes steganography, embedding a Base64-encoded DLL file within a downloaded JPG file to obfuscate its activities. Agent Tesla is a .NET-based advanced keylogger and remote access trojan (RAT) deployed in the final stage of the attack. This malware is designed to harvest sensitive information from compromised systems, communicating with a remote server to extract the collected data.
The campaign underscores the persistent threat posed by attackers leveraging known vulnerabilities, emphasizing the need for organizations to stay vigilant and update their cybersecurity measures to counter evolving threats. In a broader context, the use of old vulnerabilities in targeted campaigns is not uncommon, as threat actors continue to exploit security weaknesses that may still be present in various systems. Organizations must adopt proactive cybersecurity measures, including regular software updates and employee training, to mitigate the risks associated with phishing attacks and the exploitation of known vulnerabilities.
