CVE-2025-65495: Libcoap

High severity, CVSS 7.5. EPSS: 0.2% chance of exploitation in the next 30 days.

Integer signedness error in tls_verify_call_back() in src/coap_openssl.c in OISM libcoap 4.3.5 allows remote attackers to cause a denial of service via a crafted TLS certificate that causes i2d_X509() to return -1 and be misused as a malloc() size parameter.

Affected products

• Libcoap Libcoap: version 4.3.5 only

Published 2025-11-24. Last modified 2026-06-17.