# CVE-2026-75083: Integer underflow of the radio-reported frame length causes an out-of-bounds write in the NXP KW41Z IEEE 802.15.4 driver

Status: published. Published: 2026-10-14. Updated: 2026-11-04.

The receive path of the NXP KW41Z IEEE 802.15.4 driver, kw41z_rx() in drivers/ieee802154/ieee802154_kw41z.c, computed the payload size as pkt_len = len - KW41Z_FCS_LENGTH in a uint8_t, where len is the frame length reported by the radio. The interrupt handler kw41z_isr() obtained that length from the RX_FRAME_LENGTH field of the ZLL IRQSTS register — a copy of the PHY header length byte of the frame received over the air — and only rejected the value zero. A reported length of one therefore underflowed to pkt_len == 255.

Because the packet is allocated with NET_AF_UNSPEC on a non-Ethernet L2, net_pkt_rx_alloc_with_buffer() does not clamp the request to the interface MTU; with the default fixed-size buffer pool (CONFIG_NET_BUF_FIXED_DATA_SIZE, CONFIG_NET_BUF_DATA_SIZE=128) the allocation succeeded as a chain of two fragments. The subsequent register-to-buffer copy loops write into the first fragment only, so 255 bytes were written into a 128-byte net_buf data block, overrunning it by up to 127 bytes into adjacent network-buffer-pool memory, and reading up to 128 bytes past the end of the radio's PKT_BUFFER_RX register array.

The length field originates from an unauthenticated frame transmitted by any device within 802.15.4 radio range, and is captured by the hardware at PHY-header time — before frame filtering has completed — while the handler samples it after clearing the interrupt status, so an attacker flooding frames with a length byte of one can drive the underflow. The impact is memory corruption in the shared receive buffer pool from interrupt context, most plausibly a crash or corruption of other packets' data; the overflowing bytes are radio register contents rather than attacker-authored data, which bounds the integrity impact.

The fix rejects any length below KW41Z_FCS_LENGTH and additionally verifies net_buf_tailroom() of the first fragment before the copy loops, which also covers the CONFIG_NET_L2_OPENTHREAD variant of the size computation.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: zephyr) — https://github.com/zephyrproject-rtos/zephyr/commit/51d71864578c08eb1a1201f87b46ec81c8609d62

## Affected products and versions

- zephyrproject / zephyr (zephyr): ≥ 1.8.0; < 4.3.2 (affected, semver); ≥ 4.4.0; < 4.5.0 (affected, semver). Source: CNA: zephyr

## Severity and prioritization

- CVSS 3.1: 5.9 (medium); CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H; source: CNA: zephyr

- CVSS 3.1: 5.9 (medium); CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H; source: NVD: vulnerabilities@zephyrproject.org

- CISA KEV: No listing in collected sources

- EPSS: 0.23% as of 2026-11-03; percentile 13.82%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-191

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/zephyrproject-rtos/zephyr/commit/51d71864578c08eb1a1201f87b46ec81c8609d62 (CNA: zephyr; patch)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-2pwx-gg6f-535f (CNA: zephyr)

- https://github.com/zephyrproject-rtos/zephyr/commit/51d71864578c08eb1a1201f87b46ec81c8609d62 (vulnerabilities@zephyrproject.org)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-2pwx-gg6f-535f (vulnerabilities@zephyrproject.org)

## Provenance

- CNA: zephyr: https://www.cve.org/CVERecord?id=CVE-2026-75083; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-75083; retrieved 2026-11-04; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-75083; retrieved 2026-11-04; source updated Not reported

Revision: 61fb4bf547a7747bc4f7be78c573b3d24b7274cb3917abdcba83b92600ead3f1

Canonical: https://y2.dev/cve/CVE-2026-75083

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