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CVE-2026-12363— Out-of-bounds write in LoRaWAN fragmented transport from a fragment index of 0

Quick assessment

Affected
zephyrproject zephyr
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Zephyr Project zephyr是Zephyr Project组织开源的一个面向物联网设备的实时操作系统。 Zephyr Project zephyr 3.7.0版本至4.5.0之前版本存在缓冲区错误漏洞，该漏洞源于未验证接收到的DATA_FRAGMENT命令中的分片计数器，导致分片计数器为0时发生下溢和越界写入，可能造成解码器状态损坏和拒绝服务。

CVSS 4.2 · Medium EPSS 0.24% · P14

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
zephyrproject zephyr 3.7.0< 4.5.0 affected
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I. Basic Information for CVE-2026-12363

Vulnerability Information
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Vulnerability Title
Out-of-bounds write in LoRaWAN fragmented transport from a fragment index of 0
Source: CVE Program / CVE List V5
Vulnerability Description
The LoRaWAN Fragmented Data Block Transport service (subsys/lorawan/services/frag_transport.c) does not validate the fragment counter in a received DATA_FRAGMENT command before forwarding it to the configured decoder. In frag_transport_package_callback() the value frag_counter = hdr->frag_index_n & 0x3FFF is taken directly from the downlink payload and passed to the decoder, which derives an array index and flash offset as frag_counter - 1. DataFragment fragments are 1-indexed, so a frag_counter of 0 underflows that arithmetic. With the default Semtech/LoRaMAC-node decoder, this reaches FragDecoder.FragNbMissingIndex[fragCounter - 1] = 0; in FragDecoderProcess(), where fragCounter - 1 evaluates to -1 and writes a uint16_t zero out of bounds, just before the array and into the adjacent MatrixM2B recovery-matrix state of the static decoder object (CWE-787). A companion write derives a wild flash offset, but that path is rejected by the flash_area_write() bounds check. The in-tree low-memory decoder (frag_dec()) is not corrupted: its out-of-range bit-array and flash accesses are caught by sys_bitarray_ and flash_area_ bounds checks. The handler is the registered downlink callback for the fragmentation transport port, reachable whenever an active fragmentation session exists, so the triggering byte is attacker-influenceable LoRaWAN/FUOTA network input. Triggering it requires authenticated downlinks (LoRaWAN MAC session keys or a malicious/compromised network or FUOTA server) and an active fragmentation session. The impact is contained: corruption of decoder state and denial of the firmware-update (FUOTA) session rather than controllable memory corruption or code execution. The fix adds a transport-layer check that rejects frag_counter == 0, closing the defect for both decoder backends.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5
Vulnerability Title
Zephyr Project zephyr 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Zephyr Project zephyr是Zephyr Project组织开源的一个面向物联网设备的实时操作系统。 Zephyr Project zephyr 3.7.0版本至4.5.0之前版本存在缓冲区错误漏洞，该漏洞源于未验证接收到的DATA_FRAGMENT命令中的分片计数器，导致分片计数器为0时发生下溢和越界写入，可能造成解码器状态损坏和拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
zephyrproject zephyr 3.7.0 ~ 4.5.0 -

II. Public POCs for CVE-2026-12363

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III. Intelligence Information for CVE-2026-12363

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Patches & Fixes for CVE-2026-12363 (1)

Vendor Advisories for CVE-2026-12363 (1)

Same Patch Batch · zephyrproject · 2026-08-14 · 4 CVEs total

CVE-2026-12366 8.8 HIGH Use-after-free freeing an armed dynamically-allocated k_timer in Zephyr userspace object d
CVE-2026-12364 8.4 HIGH Missing user-space pointer validation in logging syscall z_log_msg_static_create allows ke
CVE-2026-12365 5.8 MEDIUM Use-after-free in Zephyr delayable work-queue cancellation under SMP timing race

IV. Related Vulnerabilities

Same product: zephyr
Same vendor: zephyrproject
Same weakness: CWE-787

V. Comments for CVE-2026-12363

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