Exim BDAT Vulnerability (CVE-2026-45185) Exposes GnuTLS Builds to RCE

Exim has issued critical security updates to address a severe vulnerability, tracked as CVE-2026-45185 and dubbed “Dead.Letter.” This use-after-free flaw affects specific Exim configurations, potentially leading to memory corruption and remote code execution (RCE).

According to The Hacker News, this issue primarily impacts Exim Mail Transfer Agents (MTAs) compiled with GnuTLS. Exim, an open-source MTA widely used on Unix-like systems for email handling, is a critical component in countless network infrastructures. An attacker successfully exploiting this vulnerability could gain significant control, disrupting email services or leveraging the compromise for deeper network penetration.

Defenders must prioritize patching. The attacker’s calculus here is straightforward: email infrastructure is a high-value target. A successful RCE on an MTA grants access to sensitive communications and often provides a foothold into the internal network. This isn’t just about email disruption; it’s about a clear path to data exfiltration and lateral movement.