Postfix 3.11.5, released on July 6, 2026, addresses multiple remote denial-of-service and local memory corruption vulnerabilities, many of which have been present in the codebase for over two decades. The vulnerabilities were discovered by Qualys with assistance from Anthropic's Claude Mythos Preview, which helped identify issues in the extensive C code without replacing the need for human review. The release includes three main categories of fixes: denial-of-service vulnerabilities, memory corruption issues, and various code hygiene updates, while also providing updates for older legacy branches. Postfix's design philosophy emphasizes security, maintaining a defense-in-depth architecture that has proven effective across millions of deployments worldwide

Postfix 3.11.5 Drops DoS and Memory Corruption Fixes Discovered With AI Assist

Postfix 3.11.5 landed on July 6, 2026, patching a slate of remote denial-of-service triggers and local memory corruption flaws across the widely deployed mail server. The vulnerabilities were uncovered by Qualys with research assistance from Anthropic's Claude Mythos Preview, and more than half of them have been hiding in the codebase for at least two decades. One of the defects traces back to the project's original 1997 build, though Postfix's defense-in-depth architecture means most of the issues require specific configurations to actually trigger. Alongside the security fixes, the release also updates legacy branches and addresses several code hygiene gaps tied to memory management and process isolation.

Postfix 3.11.5 Drops DoS and Memory Corruption Fixes Discovered With AI Assist @ Linux Compatible