CVE-2023-42115

The vulnerability is located in the SMTP service listening by default on TCP port 25, in the authentication (AUTH) handling mechanism. The vulnerability results from lack of proper validation of data supplied by the user, leading to an out-of-bounds write (CWE-787). An attacker can send a specially crafted SMTP packet, causing memory overwrite outside the buffer boundaries and taking control over the process execution flow.

An attacker can execute arbitrary code in the context of the Exim service account, which in practice may mean complete takeover of the mail server. Possible consequences include breach of confidentiality, integrity, and system availability.

Apply patches available from the vendor according to the references. As a temporary workaround, consider restricting access to TCP port 25 only to trusted IP addresses using a firewall and monitoring anomalous SMTP connections.

Exim — versions indicated in the vendor references (vulnerability identified as ZDI-CAN-17434 / ZDI-23-1469)