Off-by-one out-of-bounds NUL write in Zephyr LwM2M JSON string parser
Summary
| CVE | CVE-2026-14368 |
|---|---|
| State | PUBLISHED |
| Assigner | zephyr |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-08-31 19:16:45 UTC |
| Updated | 2026-09-01 15:17:11 UTC |
| Description | The LwM2M JSON content formatter's get_string() in subsys/net/lib/lwm2m/lwm2m_rw_json.c copies a parsed JSON string into a caller-supplied buffer and NUL-terminates it. The length guard used if (string_length > buflen), which accepts a string whose length is exactly buflen. After memcpy() fills the whole buffer, buf[string_length] = '\0' then writes one byte past the end of the buffer (CWE-787). The string value and its length are taken directly from the incoming CoAP payload during a LwM2M WRITE: do_write_op_json() parses the payload obtained from coap_packet_get_payload(), and get_string() is invoked from lwm2m_write_handler() (engine_get_string() in subsys/net/lib/lwm2m/lwm2m_message_handling.c) for a LWM2M_RES_TYPE_STRING resource. The destination buf/buflen is either the resource instance's fixed data buffer (res_inst->data_ptr/max_data_len) or the engine validation buffer (msg->ctx->validate_buf). A LwM2M server (the client's DTLS peer) can therefore write a string resource with a value whose length equals the target buffer size and force a one-byte overflow. The overflow is a single out-of-bounds write of the constant byte 0x00 immediately past the resource or validation buffer, corrupting the adjacent byte in memory. It is not an information leak and the written value is fixed, so it is not a direct code-execution primitive, but it can corrupt adjacent state (an adjacent resource value, a length/flag field, or a struct field) and cause data corruption or a crash. Triggering the write is deterministic; the resulting impact depends on memory layout. The fix changes the guard to string_length >= buflen, rejecting the exact-length case and aligning the JSON formatter with the other content formatters (lwm2m_rw_plain_text.c, lwm2m_rw_oma_tlv.c, lwm2m_rw_senml_json.c, lwm2m_rw_cbor.c, lwm2m_rw_senml_cbor.c), which already used the correct boundary check. |
Risk And Classification
Primary CVSS: v3.1 5.4 MEDIUM from [email protected]
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
EPSS: 0.002270000 probability, percentile 0.132780000 (date 2026-09-02)
Problem Types: CWE-193 | CWE-787 | CWE-787 bounds | CWE-193 bounds
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 5.4 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L |
| 3.1 | CNA | CVSS | 5.4 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
LowUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
LowAvailability
LowCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Zephyrproject | Zephyr | affected 3.2.0 4.4.2 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-vg53-h6qq-... | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | github.com | |
| github.com/zephyrproject-rtos/zephyr/commit/ba38f4b94337cc2c2446277ac181... | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.