CVE-2026-102720
MediumCVSS 5.3Summary
In the DHCP client (addons/dhcp/nxd_dhcp_client.c), the TLV option walk advances the offset counter 'i' by size+1 while the data pointer 'data' advances by size+2. After skipping enough options, the bound check 'i < length - 1' still passes even though the data pointer has moved past the end of the received message. As a result, the DHCP client reads roughly a kilobyte past the buffer (heap-buffer-overflow), which can be triggered by a malicious DHCP server or anyone on the LAN who answers a DISCOVER first.
Risk Assessment
The issue occurs on every boot of a DHCP client within reach of a hostile DHCP responder, while the client is still unconfigured. The out-of-bounds bytes are used to configure the interface, which can lead to information disclosure from memory and potential impact on the device's network configuration.
Recommendation
Update the component to a version containing the fix that advances 'i' by size+2 or derives the bound from the 'data' pointer instead of keeping a second counter. Until the patch is applied, consider limiting trust in LAN DHCP servers (e.g., DHCP snooping, controlled DHCP server).
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Original NVD description (English source)
A DHCP server, or anyone on the LAN who answers a DISCOVER first, can make the client read about a kilobyte past the end of the received message. The option walk keeps a pointer and an offset in step, and the only bound check uses the offset: ```c /* addons/dhcp/nxd_dhcp_client.c:7538, 7572 */ while (i < length - 1) { ... size = *(++data); /* data moves 1: type -> length byte */ data += size + 1; /* data moves size + 1 more */ i += size + 1; /* i moves only size + 1 */ } ``` A TLV option occupies size + 2 bytes. `data` is advanced by size + 2 in total, `i` by size + 1, so the offset falls one byte behind the real read position for every option the walk skips. After enough skipped options the check `i < length - 1` still holds while `data` is already past the end of the message, and the subsequent read of the type and length bytes comes from whatever follows. A single OFFER carrying a long run of skippable options is enough: ``` ERROR: AddressSanitizer: heap-buffer-overflow READ of size 1 at 0x61b000000794 thread T5 #0 _nx_dhcp_search_buffer addons/dhcp/nxd_dhcp_client.c:7541 #1 _nx_dhcp_get_option_value addons/dhcp/nxd_dhcp_client.c:7082 0x61b000000794 is located 164 bytes to the right of 1648-byte region ``` A well formed OFFER through the same path is handled normally, the client records the offer and moves to REQUESTING, so the difference is the option layout rather than the harness. The read runs in the DHCP client thread while the client is still unconfigured, so it happens on every boot in reach of a hostile DHCP responder. The values read are used to configure the interface, which is how the disclosed bytes become observable. Advance `i` by size + 2, or derive the bound from `data` rather than keeping a second counter.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS