CVE-2024-23185 is a resource exhaustion vulnerability found in Open-Xchange GmbH's OX Dovecot Pro mail server software. The issue stems from the message-header-parser component, which constructs a "full_value" buffer by concatenating smaller chunks of email header data without enforcing any size limits. This means that if an email contains very large headers—either as a single long header line or a header split across multiple lines—the buffer can grow excessively large, leading to high memory consumption. The message-parser normally reads messages in reasonably sized chunks, but the unchecked aggregation in the header parser causes unbounded memory allocation. While mail transfer agents typically enforce size limits on incoming emails, mitigating the risk of remote exploitation, users who append large emails themselves can trigger this vulnerability, potentially causing denial-of-service (DoS) conditions by exhausting server memory. This can degrade backend performance or cause crashes. The vulnerability affects all versions of Dovecot, as no version-specific fixes are noted. No public exploits have been reported, and no patches have been linked yet. The CVSS 3.1 base score is 7.5, reflecting a high severity due to the vulnerability's impact on availability, ease of exploitation (no privileges or user interaction required), and network attack vector.

For European organizations using OX Dovecot Pro as their mail server, this vulnerability poses a significant risk to mail system availability. Although remote exploitation is limited by typical MTA size restrictions, insider threats or compromised user accounts could exploit the vulnerability by appending large emails, causing service disruptions or backend instability. This could impact business communications, delay critical email delivery, and increase operational costs due to system downtime or recovery efforts. Organizations with high email traffic or those relying heavily on Dovecot for mail storage and retrieval are particularly vulnerable. Additionally, memory exhaustion could lead to cascading failures affecting other services hosted on the same infrastructure. The lack of confidentiality or integrity impact reduces risk of data breach but does not diminish the operational impact. European entities in sectors such as finance, government, and healthcare, where email availability is critical, may face compliance and reputational risks if mail services are disrupted.

To mitigate CVE-2024-23185, European organizations should implement strict header size restrictions at the mail transfer agent (MTA) level before emails reach Dovecot. Configuring MTAs like Postfix or Exim to reject or truncate emails with excessively large headers can prevent resource exhaustion. Administrators should monitor mail server logs for abnormal memory usage or unusually large emails appended by users. Applying any forthcoming patches from Open-Xchange GmbH promptly is essential once available. Additionally, enforcing user quotas and limiting the size of emails users can append reduces risk of self-inflicted DoS. Network-level protections such as rate limiting and anomaly detection on SMTP traffic can help identify and block suspicious large-header emails. Regularly auditing and updating mail server configurations to align with best practices for resource management will further reduce exposure. Finally, educating users about risks of appending large emails and monitoring for insider misuse can help prevent exploitation.