Analytics Story: WinRAR Spoofing Attack CVE-2023-38831
Description
Group-IB Threat Intelligence unit discovered a zero-day vulnerability, CVE-2023-38831, in WinRAR, a popular compression tool. Cybercriminals exploited this vulnerability to deliver various malware families, including DarkMe and GuLoader, by crafting ZIP archives with spoofed extensions, which were then distributed on trading forums. Once the malware was executed, it allowed cybercriminals to withdraw funds from brokers' accounts. RARLAB was immediately notified about the vulnerability and released a patch. Group-IB recommends users update WinRAR to the latest version, stay informed about cyber threats, be cautious with unknown attachments, enable 2FA, backup data, and follow the principle of least privilege.
Why it matters
Group-IB Threat Intelligence unit identified a critical zero-day vulnerability, CVE-2023-38831, in WinRAR, a widely used compression tool. This vulnerability was exploited by cybercriminals to craft ZIP archives containing malicious and non-malicious files, distributed on specialized trading forums. The exploit allowed them to spoof file extensions, hiding the launch of malicious scripts within an archive masquerading as a '.jpg', '.txt', or any other file format. When victims opened the specially crafted archive, it executed the malware, leading to unauthorized access to their broker accounts and enabling the cybercriminals to perform illicit financial transactions and withdraw funds. The vulnerability was discovered while researching the spread of DarkMe malware, a VisualBasic spy Trojan attributed to the financially motivated group, Evilnum. The malware was distributed alongside other malware families, such as GuLoader and Remcos RAT, via malicious ZIP archives posted on popular trading forums or distributed via file-sharing services. Despite efforts by forum administrators to warn users and disable threat actors' accounts, the cybercriminals continued to spread the malicious files, compromising devices, and leading to financial losses. Group-IB immediately notified RARLAB about the vulnerability, and they promptly responded by issuing a patch. The beta version of the patch was released on July 20, 2023, and the final updated version, WinRAR 6.23, was released on August 2, 2023. Group-IB recommends all users install the latest version of WinRAR to mitigate the risk of exploitation. In conclusion, the exploitation of the CVE-2023-38831 vulnerability highlights the constant risks associated with software vulnerabilities and the importance of remaining vigilant, keeping systems updated, and following security guidelines to avoid falling victim to such attacks. Collaboration between security researchers and software developers is essential to quickly identify and fix vulnerabilities, making it harder for cybercriminals to exploit them.
Detections
| Name | Technique | Type |
|---|---|---|
| WinRAR Spawning Shell Application | Ingress Tool Transfer | TTP |
Data Sources
| Name | Platform | Sourcetype | Source |
|---|---|---|---|
| CrowdStrike ProcessRollup2 | N/A | crowdstrike:events:sensor |
crowdstrike |
| Sysmon EventID 1 |  Windows |
xmlwineventlog |
XmlWinEventLog:Microsoft-Windows-Sysmon/Operational |
| Windows Event Log Security 4688 | Windows |
xmlwineventlog |
XmlWinEventLog:Security |
References
- https://www.group-ib.com/blog/cve-2023-38831-winrar-zero-day/
- https://nvd.nist.gov/vuln/detail/CVE-2023-38831
Source: GitHub | Version: 1