CVE-2021-24042 is a critical heap-based buffer overflow vulnerability (CWE-122) affecting multiple versions of WhatsApp across platforms, including WhatsApp Desktop prior to version 2.2146. The flaw exists in the calling logic of WhatsApp's 1:1 call feature, where an out-of-bounds write can occur if a user receives a call from a malicious actor. This vulnerability allows an attacker to overwrite memory outside the intended buffer boundaries, potentially leading to arbitrary code execution, complete compromise of the affected application, and system-level impacts. The vulnerability has a CVSS v3.1 score of 9.8, indicating a critical severity with network attack vector, no required privileges or user interaction, and impacts on confidentiality, integrity, and availability. Although no known exploits have been reported in the wild, the ease of exploitation combined with the widespread use of WhatsApp Desktop and related mobile versions makes this a significant threat. The vulnerability affects WhatsApp for Android, iOS, KaiOS, and Desktop, emphasizing the broad attack surface. Successful exploitation could allow remote attackers to execute arbitrary code, steal sensitive communications, or disrupt service availability without user interaction or authentication, making it highly dangerous.

For European organizations, the impact of CVE-2021-24042 could be severe. WhatsApp is widely used for both personal and professional communications across Europe, including by employees, executives, and third parties. Exploitation could lead to unauthorized access to confidential business communications, intellectual property theft, and potential lateral movement within corporate networks if WhatsApp Desktop is used on corporate endpoints. The critical nature of the vulnerability means attackers could gain full control over affected devices, leading to data breaches, espionage, or ransomware deployment. The disruption of communication channels could also affect operational continuity. Given the cross-platform nature of the vulnerability, organizations with Bring Your Own Device (BYOD) policies or remote workforces are particularly at risk. Furthermore, sectors with high regulatory requirements for data protection, such as finance, healthcare, and government, could face compliance violations and reputational damage if exploited.

European organizations should implement a multi-layered mitigation strategy: 1) Immediate patching: Ensure all WhatsApp Desktop clients and mobile versions are updated to the latest patched versions (Desktop >= 2.2146, Android >= 2.21.23, iOS >= 2.21.230, KaiOS >= 2.2143). 2) Network controls: Restrict or monitor incoming WhatsApp call traffic at network boundaries where feasible, especially from unknown or untrusted contacts. 3) Endpoint protection: Deploy advanced endpoint detection and response (EDR) solutions capable of detecting anomalous behavior indicative of exploitation attempts. 4) User awareness: Educate users about the risks of accepting calls from unknown contacts and encourage cautious use of communication apps. 5) Application control: Where possible, limit the installation or use of WhatsApp Desktop on critical corporate endpoints or isolate it within secure environments. 6) Incident response readiness: Prepare for potential exploitation by establishing monitoring for suspicious WhatsApp-related activity and having response plans in place. These steps go beyond generic advice by focusing on both patch management and operational controls tailored to the threat vector.