---
id: CVE-2026-13479
title: Out-of-bounds read in LoRaWAN clock-sync AppTimeAns downlink handler
summary: >-
  The LoRaWAN application-layer clock-synchronization service parses downlinks
  in clock_sync_package_callback() (subsys/lorawan/services/clock_sync.c). Its
  command loop only guarantees that the one-byte command id is in bounds; for
  the CLO…
severity: low
cvss: 3.1
cvssVector: 'CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N'
cvssSource: cna
cwe:
  - CWE-125
vendor: zephyrproject
product: zephyr
affected:
  - zephyr >= 3.3.0 < 4.3.2
  - zephyr >= 4.4.0 < 4.4.2
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-08-26T15:44:08.607894Z'
published: '2026-08-26'
updated: '2026-11-04'
sourceUpdated: '2026-11-04T04:59:59.325Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-13479'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/3d578067652b12993bca13fb8e07dc45d062d4a5
    label: Fix commit
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-2m6g-p3vx-p2fh
    label: GHSA-2m6g-p3vx-p2fh
tags:
  - cve.org
epss: 0.00226
epssPercentile: 0.13426
ingestedAt: '2026-11-05T20:33:06.708Z'
---

## Overview

The LoRaWAN application-layer clock-synchronization service parses downlinks in clock_sync_package_callback() (subsys/lorawan/services/clock_sync.c). Its command loop only guarantees that the one-byte command id is in bounds; for the CLOCK_SYNC_CMD_APP_TIME (AppTimeAns) command the handler then reads a 4-byte time correction via sys_get_le32() plus a 1-byte token without checking that 5 bytes remain in the receive buffer (len - rx_pos). A short or crafted AppTimeAns therefore reads up to 5 bytes past the end of the decrypted payload.

The payload (rx_buf/len) is the decrypted application frame delivered to the registered downlink callback (mcps_indication->Buffer/BufferSize). Reaching the handler requires a frame on the clock-sync port that passes LoRaWAN's MAC integrity check and FRMPayload decryption, so the practical attacker is a malicious or compromised network/application server (the designated sender of AppTimeAns) or a party holding the session keys, rather than an arbitrary radio listener.

The over-read is bounded: the backing store is a fixed 255-byte static buffer, so the few stray bytes do not fault, and the read values (time_correction, token) are used only internally and never transmitted, so there is no disclosure to the attacker and no crash. The sole effect is that a stale token matching ctx.req_token can apply a garbage time_correction to the device's own clock offset (ctx.time_offset), a minor integrity impact confined to the victim's time estimate. The fix adds an explicit length check that drops a too-short AppTimeAns. Note the sibling one-byte reads in the periodicity and force-resync handlers remain unguarded with the same negligible impact.

## Affected

- `zephyr >= 3.3.0 < 4.3.2`
- `zephyr >= 4.4.0 < 4.4.2`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.