CVE-2025-34468: Libcoap

Critical severity, CVSS 9.8. EPSS: 0.7% chance of exploitation in the next 30 days.

libcoap versions up to and including 4.3.5, prior to commit 30db3ea, contain a stack-based buffer overflow in address resolution when attacker-controlled hostname data is copied into a fixed 256-byte stack buffer without proper bounds checking. A remote attacker can trigger a crash and potentially achieve remote code execution depending on compiler options and runtime memory protections. Exploitation requires the proxy logic to be enabled (i.e., the proxy request handling code path in an application using libcoap).

Affected products

• Libcoap Libcoap: up to and including 4.3.5

Published 2025-12-31. Last modified 2026-09-23.