A high-severity zero-day vulnerability has been identified in the file archive and compression tool for Windows, WinRAR. WinRAR is used to backup and compress data, reduce the size of attachments for email, uncompress RAR, ZIP, and other files downloaded from the internet, as well as create new archives in the RAR and ZIP file formats. The flaw, tracked as CVE-2023-40477, is described as an improper validation of inputs vulnerability that could allow an attacker to access data outside the bounds of an allocated memory buffer in backup volumes. If successfully exploited, this vulnerability could allow threat actors to conduct remote code execution (RCE) through vulnerable instances of WinRAR. Although the vulnerability is quite severe if successfully exploited, it received a CVSS score of 7.8/10 due to successful exploitation requiring user interaction. A threat actor would first need to trick the victim into visiting a malicious page or opening a maliciously crafted archive file via a social engineering attack such as phishing. The vulnerability exists in all versions of WinRAR prior to 6.23. CTIX analysts recommend that users ensure they’re running the most recent version of the software.