This vulnerability allows remote attackers to execute arbitrary code on affected
installations of Exim. Authentication is not required to exploit this
vulnerability.

The specific flaw exists within the smtp service, which listens on TCP port 25
by default. The issue results from the lack of proper validation of
user-supplied data, which can result in a write past the end of a buffer. An
attacker can leverage this vulnerability to execute code in the context of the
service account.

06/06/22 – ZDI requested a PSIRT contact.

06/14/22 – ZDI reported the vulnerability to the vendor.

04/25/23 – ZDI asked for an update.

04/25/23 – The vendor asked us to re-send the reports.

05/10/23 – ZDI sent the vulnerability to the vendor.

09/25/23 – ZDI asked for an update and informed the vendor that we intend to
publish the case as a zero-day advisory on 09/27/23.

-- Mitigation: Given the nature of the vulnerability, the only salient
mitigation strategy is to restrict interaction with the application.

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2023-42115