libcoap up to 4.3.5a CBOR Parser src/oscore/oscore_cbor.c get_byte_inc out-of-bounds

Summaryinfo

A vulnerability identified as problematic has been detected in libcoap up to 4.3.5a. This affects the function get_byte_inc of the file src/oscore/oscore_cbor.c of the component CBOR Parser. This manipulation causes out-of-bounds. The identification of this vulnerability is CVE-2026-29013. It is possible to initiate the attack remotely. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in libcoap up to 4.3.5a. Affected by this vulnerability is the function get_byte_inc of the file src/oscore/oscore_cbor.c of the component CBOR Parser. The manipulation with an unknown input leads to a out-of-bounds vulnerability. The CWE definition for the vulnerability is CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

libcoap contains out-of-bounds read vulnerabilities in OSCORE Appendix B.2 CBOR unwrap handling where get_byte_inc() in src/oscore/oscore_cbor.c relies solely on assert() for bounds checking, which is removed in release builds compiled with NDEBUG. Attackers can send crafted CoAP requests with malformed OSCORE options or responses during OSCORE negotiation to trigger out-of-bounds reads during CBOR parsing and potentially cause heap buffer overflow writes through integer wraparound in allocation size computation.

The weakness was shared by Kazuma Matsumoto as b7847c4dbb0dbee7c90b09a673d4cae256f03718. The advisory is shared at github.com. This vulnerability is known as CVE-2026-29013 since 03/03/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available.

Upgrading to version 4.3.5b eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-23535). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• libcoap

Version

• 4.3.5a

CPE 2.3info

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CPE 2.2info

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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