Exim before 4.100.1, when certain non‑default TLS settings are used with GnuTLS, can trigger a use‑after‑free. This flaw allows an attacker to read or corrupt memory that has already been freed, potentially leading to unpredictable program behavior, including crashes or other forms of denial of service. The vulnerability is classified as CWE‑416.

Affected systems are Exim mail servers running any version prior to 4.100.1. The issue appears when non‑default GnuTLS TLS configurations are applied; all earlier releases are vulnerable until the version that includes the fix is deployed.

With a CVSS score of 3.7 the risk is considered moderate; the EPSS score is not available, and the flaw is not listed in CISA KEV. The attack vector is likely remote via a TLS connection, as the vulnerability is exercised through non‑default TLS settings. Successful exploitation could lead to memory corruption, resulting in crashes or irregular behavior, but the current data does not indicate direct code execution or data exfiltration.