CVE-2026-5855: Contiki-NG

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

Contiki-NG's LwM2M TLV parser lwm2m_tlv_read() in os/services/lwm2m/lwm2m-tlv.c ignores its caller-supplied buffer length argument and reads up to six bytes from the input buffer with no bounds check. The caller in lwm2m-engine.c iterates while there is at least one byte remaining, so a crafted CoAP WRITE to any LwM2M endpoint whose final TLV supplies exactly one byte triggers up to five out-of-bounds reads of heap memory adjacent to the CoAP input buffer, disclosing memory contents (including key material and peer addresses) through the parsed tlv->id, tlv->length, and tlv->value fields. Corrupted tlv_len derived from the out-of-bounds memory further corrupts the caller's parse offset. In LwM2M NoSec mode, the default for constrained devices, no authentication is required.

Affected products

• Contiki-NG Contiki-NG: before f1673b5766d4d4d514cefb8a0350f43653574997 (fixed in f1673b5766d4d4d514cefb8a0350f43653574997)

Published 2026-08-06. Last modified 2026-09-16.