CVE-2026-102714 in NetX Duo
Summary
by MITRE • 09/29/2026
`_nx_icmpv6_validate_options()` scans the option area with `while (length > 2)` (`common/src/nx_icmpv6_validate_options.c:79`). An area whose size leaves a one- or two-byte residue exits the loop with that tail unexamined; the residue is not negative, so the function returns `NX_SUCCESS`. Its zero-length rejection never sees those bytes.
Every consumer then re-walks the same area, reading a two-byte option header at the residue and subtracting `nx_icmpv6_option_length << 3` with no zero check and no remaining-length check. Three outcomes follow, selected by bytes the attacker controls.
**Zero length byte.** The walker subtracts zero and advances zero. All four handlers loop forever — `_nx_icmpv6_process_ra` (`nx_icmpv6_process_ra.c:245, :528`), `_nx_icmpv6_process_ns` (`:251, :329`), `_nx_icmpv6_process_na` (`:147, :156`) and `_nx_icmpv6_process_redirect` (`:247, :350`). The walk runs in the IP thread, which is the highest-priority thread and does not yield inside the loop, so the system stops until a watchdog reset and the frame can be replayed after each one.
**Non-zero length byte on a short residue.** The three unsigned counters underflow — `2 - 8` becomes `0xFFFFFFFA` — and the walk continues past the packet buffer, reading until it faults or meets a zero length byte and freezes. The Router Advertisement counter is signed and exits cleanly in this case.
**One-byte residue.** The walker reads a two-byte option header, over-reading one byte.
During a runaway walk, stray bytes parsing as a link-layer address option are copied into the neighbor cache (`nx_icmpv6_process_ns.c:280, :293`) and subsequently used as the destination MAC for frames to that neighbour, placing off-packet memory on the link. Confirmed by inspection, not reproduced.
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability resides in the ICMPv6 option validation logic within NetX Duo, specifically affecting the handling of trailing bytes during packet processing. The function _nx_icmpv6_validate_options employs a loop condition that checks if the remaining length is greater than two bytes to process options. When an incoming ICMPv6 message contains an area where the size leaves only one or two bytes at the end, this validation routine exits the loop prematurely without examining these residual bytes. Because the residue length is not negative, the function incorrectly returns NX_SUCCESS, indicating that the packet structure is valid despite leaving unvalidated data in a state that subsequent processing functions will misinterpret. This initial flaw creates a discrepancy between what was validated and what is actually processed by the consumer functions responsible for handling specific ICMPv6 message types such as Router Advertisements, Neighbor Solicitations, Neighbor Advertisements, and Redirects.
When these consumer functions re-walk the option area to process individual options, they read a two-byte header from the residue without performing adequate bounds checking or zero-length validation. The behavior diverges based on the specific byte values present in this unvalidated tail section. If the length byte is interpreted as zero, the processing loop fails to advance its pointer and instead enters an infinite loop within the IP thread context. Since the IP thread operates at a high priority level and does not yield control during these loops, the system effectively hangs until a hardware watchdog timer triggers a reset. This results in a Denial of Service condition where the device becomes unresponsive to legitimate network traffic until it is manually or automatically rebooted, allowing an attacker to repeatedly replay malicious frames to maintain this state of denial of service.
In scenarios where the residue contains non-zero length bytes that result in underflow when subtracting from unsigned counters, such as calculating option lengths by shifting bits and subtracting fixed values, the arithmetic results in extremely large positive numbers due to two's complement representation issues. For example, a small remaining value minus eight can wrap around to nearly four billion bytes. This causes the parser to continue reading memory far beyond the boundaries of the allocated packet buffer. The walk continues until it either encounters a fault that crashes the system or finds a zero-length byte by chance in adjacent memory, at which point it freezes again. While some counters like those for Router Advertisements are signed and may exit cleanly under these conditions, others relying on unsigned arithmetic lead to out-of-bounds reads with potentially catastrophic consequences for system stability.
A more severe consequence arises when the residue consists of exactly one byte or specific multi-byte patterns that allow the parser to interpret stray memory contents as valid option headers. In particular, if bytes from outside the packet buffer are parsed as a link-layer address option, they may be copied into the neighbor cache via functions like _nx_icmpv6_process_ns. This results in an out-of-bounds write or read depending on implementation details, but critically it places arbitrary memory contents onto the network interface controller's transmission queue. Subsequent frames sent to that specific neighbor will use these corrupted MAC addresses as destinations, effectively transmitting off-packet memory over the link layer. Although this specific outcome has been confirmed through code inspection rather than live reproduction, it represents a critical integrity and confidentiality risk, potentially allowing an attacker to exfiltrate sensitive data from system memory or disrupt network communications by injecting malformed frames into the local area network.
This vulnerability maps directly to CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write in cases where invalid options are processed beyond buffer limits, as well as CWE-674 Uncontrolled Recursion which manifests here as unbounded loops due to logic errors rather than recursive function calls. From an ATT&CK perspective, this aligns with T1499 Endpoint Denial of Service and potentially T1059 Command Line Interface if the system instability leads to further exploitation vectors during recovery or reboot cycles. Mitigation strategies must focus on rigorous input validation at the packet parsing layer. Developers should ensure that all option length calculations account for remaining buffer space before processing, explicitly checking for zero-length options to prevent infinite loops and verifying bounds against the total packet size before copying data into structures like the neighbor cache. Updating to a patched version of NetX Duo that corrects these arithmetic checks and loop termination conditions is essential to restore secure operation.