# CVE-2026-13479: Out-of-bounds read in LoRaWAN clock-sync AppTimeAns downlink handler

Status: published. Published: 2026-08-26. Updated: 2026-11-04.

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.

## 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/3d578067652b12993bca13fb8e07dc45d062d4a5
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: vulnerabilities@zephyrproject.org) — https://github.com/zephyrproject-rtos/zephyr/commit/3d578067652b12993bca13fb8e07dc45d062d4a5
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: vulnerabilities@zephyrproject.org) — https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-2m6g-p3vx-p2fh

## Affected products and versions

- zephyrproject / zephyr (zephyr): ≥ 3.3.0; < 4.3.2 (affected, semver); ≥ 4.4.0; < 4.4.2 (affected, semver). Source: CNA: zephyr

## NVD configuration conditions

Affected CPE matches depend on the following AND/OR and negation conditions:

```json
[
  {
    "negate": false,
    "nodes": [
      {
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:o:zephyrproject:zephyr:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "4.4.2",
            "versionStartIncluding": "3.3.0",
            "vulnerable": true
          }
        ],
        "negate": false,
        "operator": "OR"
      }
    ],
    "operator": "OR"
  }
]
```

## Severity and prioritization

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

- CVSS 3.1: 4.3 (medium); CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N; source: NVD: nvd@nist.gov

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

- CISA KEV: No listing in collected sources

- EPSS: 0.23% as of 2026-11-03; percentile 13.38%

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

- Weaknesses: CWE-125

## Exploit evidence

- exploit: https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-2m6g-p3vx-p2fh (vulnerabilities@zephyrproject.org)

## References

- https://github.com/zephyrproject-rtos/zephyr/commit/3d578067652b12993bca13fb8e07dc45d062d4a5 (CNA: zephyr; patch)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-2m6g-p3vx-p2fh (CNA: zephyr)

- https://github.com/zephyrproject-rtos/zephyr/commit/3d578067652b12993bca13fb8e07dc45d062d4a5 (vulnerabilities@zephyrproject.org; Patch)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-2m6g-p3vx-p2fh (vulnerabilities@zephyrproject.org; Exploit, Patch, Vendor Advisory)

## Provenance

- CNA: zephyr: https://www.cve.org/CVERecord?id=CVE-2026-13479; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-13479; retrieved 2026-11-04; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-13479; retrieved 2026-11-04; source updated Not reported

Revision: de401ba727e7c9f2961994eee609bdecb9bf493ab5cd2875550fcdf22da307ba

Canonical: https://y2.dev/cve/CVE-2026-13479

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