The broker in Eclipse Mosquitto 1.3.2 through 2.x before 2.0.16 has a memory leak that can be abused remotely when a client sends many QoS 2 messages with duplicate message IDs, and fails to respond to PUBREC commands. This occurs because of mishandling of EAGAIN from the libc send function.
https://www.debian.org/security/2023/dsa-5511
https://security.gentoo.org/glsa/202401-09
https://mosquitto.org/blog/2023/08/version-2-0-16-released/
https://github.com/eclipse/mosquitto/compare/v2.0.15...v2.0.16
https://github.com/eclipse/mosquitto/commit/6113eac95a9df634fbc858be542c4a0456bfe7b9