CVE-2024-23184 is a resource exhaustion vulnerability in Open-Xchange GmbH's OX Dovecot Pro, a widely used mail server software. The issue stems from the software's handling of email address headers—specifically, when an email contains an unusually large number of address header lines such as From, To, Cc, and Bcc. Parsing these headers is CPU intensive; tests show that 100,000 header lines can cause 12 seconds of CPU usage, while 500,000 lines can take up to 18 minutes to parse. This excessive processing can be triggered remotely by sending crafted emails to the target system, leading to denial-of-service (DoS) conditions by exhausting CPU resources. The vulnerability does not affect confidentiality or integrity but impacts availability. It requires no user interaction and can be exploited remotely without authentication, increasing its risk profile. No public exploits have been reported yet, but the vulnerability is recognized and published with a CVSS 3.1 base score of 5.0 (medium severity). Mitigation involves implementing restrictions on the number of address headers at the mail transfer agent (MTA) level before the email is processed by Dovecot, effectively limiting resource consumption. This approach is necessary because the vulnerability lies in the parsing logic of Dovecot Pro itself. The vulnerability was reserved in January 2024 and published in September 2024, indicating recent discovery and disclosure.

For European organizations, this vulnerability poses a risk primarily to the availability of email services. Organizations relying on OX Dovecot Pro for mail delivery and storage could experience service degradation or outages if targeted by attackers sending emails with excessively large numbers of address headers. This could disrupt business communications, lead to operational downtime, and impact productivity. Critical sectors such as finance, government, healthcare, and large enterprises with high email traffic volumes are particularly vulnerable to service interruptions. Since the attack vector is external email delivery, organizations with public-facing mail servers are at risk. The vulnerability does not compromise data confidentiality or integrity but can cause denial-of-service conditions that may require emergency response and incident handling. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits over time. European organizations must consider this vulnerability in their risk assessments and incident response planning to maintain email service continuity.

To mitigate CVE-2024-23184 effectively, organizations should implement strict limits on the number of address headers allowed in incoming emails at the mail transfer agent (MTA) level, such as Postfix, Exim, or Sendmail, before messages reach OX Dovecot Pro. This can be done by configuring header size and count restrictions or employing filtering rules to reject or quarantine suspicious emails with abnormally large header counts. Monitoring email traffic for unusual patterns in header counts can provide early detection of exploitation attempts. Additionally, organizations should ensure their OX Dovecot Pro installations are updated promptly once patches become available from Open-Xchange GmbH. Network-level protections such as rate limiting and connection throttling on SMTP ports can reduce the volume of potentially malicious emails. Deploying email security gateways with advanced filtering capabilities can also help block malformed or suspicious emails. Finally, maintaining comprehensive logging and alerting on mail server performance metrics will aid in identifying resource exhaustion events early and enable rapid incident response.