Input-Validation Flaw in Zephyr's IPv6 Neighbor Discovery Process

CVE-2026-7656

What is CVE-2026-7656?

The vulnerability arises from a flaw in the IPv6 Neighbor Discovery handlers within Zephyr RTOS, where an erroneous boolean expression allows an attacker to manipulate legitimate Neighbor Discovery (ND) messages. Specifically, the misuse of operator precedence in the validity checks permits crafted Router Advertisement, Neighbor Solicitation, and Neighbor Advertisement messages to be processed without proper validation. This bypass enables an adjacent attacker to reconfigure critical network parameters, such as routing configurations and timer settings, and conduct further attacks such as neighbor-cache poisoning. The flaw has been present in the code since its introduction and affects all versions up to 4.4.0. A fix has been implemented by refining the condition checks to ensure any failed verification results in packet rejection, thereby enhancing the security of the system.

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