Exim before 4.100.1 contains an out-of-bounds write when the Proxy-Protocol is used with an attacker-controlled proxy, potentially leading to memory corruption. The weakness is an instance of CWE-787, where improper bounds checking allows a malicious input to overwrite adjacent memory. This can compromise confidentiality, integrity, and availability if exploited.

All Exim installations running version 4.100.0 or earlier are affected. The vulnerability applies to the Exim email server product as listed by the CNA.

The vulnerability carries a CVSS score of 7, indicating moderate to high severity. The EPSS score is not available, and the issue is not listed in the CISA KEV catalog, suggesting no widespread exploitation is known. The likely attack requires an attacker to control a proxy that forwards Proxy-Protocol packets to the vulnerable Exim instance; successful exploitation could result in memory corruption and potentially remote code execution. No official workaround is provided in the advisory.