A critical zero-day vulnerability (CVE-2024-45519) has been discovered in Synacor’s Zimbra Collaboration, specifically in the postjournal service. This vulnerability allows attackers to achieve unauthenticated remote code execution (RCE) by sending specially crafted emails. The vulnerability lies in the postjournal SMTP parsing service, which is not enabled by default but is still considered a significant threat. Organizations are urged to patch their Zimbra installations as soon as possible to protect against active exploitation. CISA has flagged CVE-2024-45519 as actively exploited, highlighting the urgency of the situation. Proof-of-concept (PoC) exploits have been demonstrated, showcasing the vulnerability’s potential for malicious activity. The vulnerability stems from a lack of proper input sanitization, which allows attackers to inject arbitrary commands into the postjournal service. This highlights the importance of secure coding practices and robust input validation to prevent such vulnerabilities from emerging.