CVE-2026-102720

DHCP client option walk drifts one byte per skipped option, reading past the received message and past the saved options buffer

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Published Sep 29, 2026 CVSS 4.0 · 5.3 Medium EPSS < 1% KEV · Not listed
Description
In Eclipse ThreadX NetX Duo versions 6.0 through 6.5.2.202603a, the DHCP client's option walk advances its offset one byte less than its read pointer for every option it skips. A DHCP server, or any host on the link that answers first, can make the client read up to about a kilobyte past the received message, and the same walk copies out-of-bounds bytes into the application's buffer when it retrieves a user option.

Analysis

AI-generated

Technical impact

The DHCP client in Eclipse ThreadX NetX Duo incorrectly adjusts its offset by one byte less than its read pointer for each skipped option, creating an out‑of‑bounds read and write that satisfies CWE‑125 and CWE‑193. A malicious DHCP server or any host that responds first can cause the client to read up to about one kilobyte past the end of the received message, and the then‑copied data may overwrite the application's buffer. This heap‑buffer overflow can corrupt configuration memory or trigger arbitrary code execution on the device.

Affected Systems

Eclipse ThreadX NetX Duo versions 6.0 through 6.5.2.202603a are affected. All firmware that includes the DHCP option‑walking code in these releases is at risk.

Risk and Exploitability

The CVSS score of 5.3 indicates a moderate severity weakness, and the EPSS score of < 1% shows a very low but non‑zero probability of exploitation. The vulnerability is not listed in CISA KEV. An attacker that can inject crafted DHCP traffic on the local network can induce the overflow during boot or while the client processes an OFFER, potentially leading to memory corruption, a system crash, or remote code execution depending on the device’s memory state.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Apply the latest Eclipse ThreadX/NetX Duo patch or updated firmware that repairs the DHCP option parsing logic
  • Disable the DHCP client or switch to a static IP configuration until the patch is applied to prevent the overflow on boot
  • Block unsolicited DHCP responses or enable DHCP snooping on network switches to guard against unauthorized hosts

Generated by OpenCVE AI on November 4, 2026 at 15:22 UTC.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Description 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. In Eclipse ThreadX NetX Duo versions 6.0 through 6.5.2.202603a, the DHCP client's option walk advances its offset one byte less than its read pointer for every option it skips. A DHCP server, or any host on the link that answers first, can make the client read up to about a kilobyte past the received message, and the same walk copies out-of-bounds bytes into the application's buffer when it retrieves a user option.
Title DHCP client option walk drifts one byte per skipped option, reading past the received message and past the saved options buffer
Weaknesses CWE-193
Type Values Removed Values Added
First Time appeared Eclipse
Eclipse threadx Netx Duo
Vendors & Products Eclipse
Eclipse threadx Netx Duo
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}
Type Values Removed Values Added
Description 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.
Weaknesses CWE-125
References
Metrics cvssV4_0

{'score': 5.3, 'vector': 'CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N'}
Weaknesses

Sources

Status
PUBLISHED
Assigner
eclipse
Published
Updated
Nov 4, 2026, 9:42 AM
Reserved
Sep 29, 2026, 4:15 PM

View source JSON

Updated
Sep 29, 2026, 6:37 PM

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Status
Awaiting Analysis
Published
Sep 29, 2026, 6:17 PM
Modified
Nov 4, 2026, 10:17 AM

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No data.

Updated
Nov 4, 2026, 3:30 PM

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