CVE-2026-13479: Zephyr Out-of-Bounds Read (CVSS 4.3)

Description

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.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

0.15%

4.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-125

Affected Software

Vendor	Product	Versions
Zephyrproject	Zephyr	>= 3.3.0, < 4.4.2

References

https://github.com/zephyrproject-rtos/zephyr/commit/3d578067652b12993bca13fb8e07dc45d062d4a5Patch
https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-2m6g-p3vx-p2fhExploit, Patch, Vendor Advisory

Timeline

Published: Aug 26, 2026
Last Modified: Aug 31, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-13479?

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.

How severe is CVE-2026-13479?

CVE-2026-13479 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.15% probability of exploitation in the next 30 days.

How do I fix CVE-2026-13479?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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