CVE-2026-5855 Contiki-NG LwM2M TLV Parser Out-of-Bounds Read via Unchecked Buffer Length in lwm2m_tlv_read
Attackers can read adjacent heap memory, including keys, via crafted CoAP packets in Contiki-NG LwM2M TLV parser.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-5855?
CVE-2026-5855 is a high-severity vulnerability in Contiki-NG, published on 6 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-125
Which versions are affected by CVE-2026-5855?
How do I fix CVE-2026-5855?
No fix has been published for CVE-2026-5855 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-5855 being exploited?
There is no known exploitation of CVE-2026-5855 in the wild and no public exploit code.
Sources
Also known as GHSA-ch5q-j8ff-mq34.