CVE-2020-12886: Arm Mbed OS

Critical severity, CVSS 9.1. EPSS: 1.4% chance of exploitation in the next 30 days.

A buffer over-read was discovered in the CoAP library in Arm Mbed OS 5.15.3. The CoAP parser is responsible for parsing received CoAP packets. The function sn_coap_parser_options_parse() parses the CoAP packet header starting from the message token. The length of the token in the received message is provided in the first byte parsed by the sn_coap_parser_options_parse() function. The length encoded in the message is not validated against the actual input buffer length before accessing the token. As a result, memory access outside of the intended boundary of the buffer may occur.

Affected products

• Arm Mbed OS: version 5.15.3 only

Published 2020-06-18. Last modified 2026-06-17.