Description
The Nuvoton NPCX eSPI driver parses Target-Attached-Flash (TAF) requests in espi_taf_parse() (drivers/espi/espi_npcx.c), taking the 12-bit length field directly out of the request header in the FLASHRXBUF FIFO. For write and RPMC OP1 requests it copied DIV_ROUND_UP(len, 4) words into struct espi_taf_pckt.src, a fixed 16-word (64-byte) member of a static structure, without ever comparing the length against that buffer or against the negotiated eSPI receive payload size (rx-plsize, 64 bytes on all in-tree NPCX/NPCK SoCs). Both the loop counter and the word count were uint8_t, so the copy ran up to 255 iterations.

An eSPI controller that emits a flash request whose header claims a payload larger than the negotiated maximum therefore drives up to 239 32-bit stores past the end of the structure — roughly 956 bytes of out-of-bounds write into .bss — from the eSPI flash receive interrupt handler, while the source reads walk past the end of the 18-word FLASHRXBUF register array into neighbouring eSPI registers. The same unvalidated length was then passed on to flash_write() in espi_taf_npcx_flash_write() with the 64-byte src buffer as source, reading up to 4 KB of adjacent controller SRAM into SPI flash at a host-chosen address, where the host can read it back. A related fixed-size stack buffer in taf_npcx_completion_handler() was overflowed by four bytes on the maximum-size completion path on SoCs whose tx-plsize is 64.

The defect is reachable only from the eSPI host side, and only by a request that violates the negotiated payload size, so it requires host firmware or bus-level control rather than ordinary host software; a compliant maximum-length write fits the buffer exactly and is handled correctly. Because TAF exists specifically so that the embedded controller arbitrates host access to shared flash (espi_taf_check_read_protect() / espi_taf_check_write_protect()), corrupting controller memory from a host-supplied field crosses the trust boundary the feature asserts; consequences range from controller crash or hang to corruption of driver state that gates the flash protection regions.

The fix widens the counters, rejects any request whose word count exceeds both ARRAY_SIZE(FLASHRXBUF) - NPCX_ESPI_FLASH_HEADER_ADDRESS_LEN and NPCX_TAF_RX_PAYLOAD_WORDS (derived from the devicetree rx-plsize), marks such packets with a new invalid_flag so espi_taf_work() answers them with an unsuccessful completion instead of processing them, bounds the transmit payload against FLASHTXBUF, and adds a default case for unsupported cycle types. Only configurations with CONFIG_ESPI_TAF enabled on an NPCX/NPCK target are affected; no in-tree board enables it by default.
Published: 2026-10-21
Score: 6.3 Medium
EPSS: < 1% Very Low
KEV: No
Impact: Memory corruption on the embedded controller
Action: Immediate patch
AI Analysis

Impact

The vulnerability is an out-of-bounds write in the Nuvoton NPCX eSPI driver that occurs when the driver parses Target‑Attached‑Flash requests. The 12‑bit length field in the request header is copied directly into a 64‑byte buffer without validation, allowing up to 239 32‑bit writes past the end of the structure. This can overwrite nearby controller memory, cause a crash or hang, and bypasses the flash protection checks that the eSPI TAF feature is designed to enforce. The outcome is a compromise of the embedded controller’s state and the ability to write arbitrary data to flash at host‑chosen locations.

Affected Systems

The flaw appears in the Zephyr RTOS Nuvoton NPCX eSPI driver (drivers/espi/espi_npcx.c). It affects Nuvoton NPCX and NPCK series SoCs when the CONFIG_ESPI_TAF configuration is enabled. No in‑tree Zephyr boards enable the feature by default, so the issue is limited to custom builds or boards that explicitly enable eSPI TAF support.

Risk and Exploitability

The CVSS score is 6.3, indicating moderate severity. EPSS is not available, and the vulnerability is not in the CISA KEV catalog, so the probability of imminent exploitation is unclear. Exploitation requires malicious host firmware or a host that can send an oversized eSPI packet, which is typically beyond the reach of ordinary host software. Therefore, while the potential impact is significant—controller memory corruption, flash protection bypass—actual exploitation is limited to environments where the host controls the eSPI bus or runs untrusted firmware.

Generated by OpenCVE AI on October 22, 2026 at 04:50 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Apply the Zephyr security patch that fixes espi_taf_parse and bounds the receive and transmit buffers (commit 1a8a0839c557a4aaa7572eb5d4948abde307b39f).
  • Disable CONFIG_ESPI_TAF in Zephyr builds if the feature is not required, to prevent any risk from this execution path.
  • Ensure that host firmware validates the negotiated payload size and rejects packets that exceed the eSPI receive payload limit; update host firmware accordingly.

Generated by OpenCVE AI on October 22, 2026 at 04:50 UTC.

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History

Fri, 23 Oct 2026 22:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Thu, 22 Oct 2026 10:45:00 +0000

Type Values Removed Values Added
First Time appeared Zephyrproject
Zephyrproject zephyr
Vendors & Products Zephyrproject
Zephyrproject zephyr

Wed, 21 Oct 2026 18:30:00 +0000

Type Values Removed Values Added
Description The Nuvoton NPCX eSPI driver parses Target-Attached-Flash (TAF) requests in espi_taf_parse() (drivers/espi/espi_npcx.c), taking the 12-bit length field directly out of the request header in the FLASHRXBUF FIFO. For write and RPMC OP1 requests it copied DIV_ROUND_UP(len, 4) words into struct espi_taf_pckt.src, a fixed 16-word (64-byte) member of a static structure, without ever comparing the length against that buffer or against the negotiated eSPI receive payload size (rx-plsize, 64 bytes on all in-tree NPCX/NPCK SoCs). Both the loop counter and the word count were uint8_t, so the copy ran up to 255 iterations. An eSPI controller that emits a flash request whose header claims a payload larger than the negotiated maximum therefore drives up to 239 32-bit stores past the end of the structure — roughly 956 bytes of out-of-bounds write into .bss — from the eSPI flash receive interrupt handler, while the source reads walk past the end of the 18-word FLASHRXBUF register array into neighbouring eSPI registers. The same unvalidated length was then passed on to flash_write() in espi_taf_npcx_flash_write() with the 64-byte src buffer as source, reading up to 4 KB of adjacent controller SRAM into SPI flash at a host-chosen address, where the host can read it back. A related fixed-size stack buffer in taf_npcx_completion_handler() was overflowed by four bytes on the maximum-size completion path on SoCs whose tx-plsize is 64. The defect is reachable only from the eSPI host side, and only by a request that violates the negotiated payload size, so it requires host firmware or bus-level control rather than ordinary host software; a compliant maximum-length write fits the buffer exactly and is handled correctly. Because TAF exists specifically so that the embedded controller arbitrates host access to shared flash (espi_taf_check_read_protect() / espi_taf_check_write_protect()), corrupting controller memory from a host-supplied field crosses the trust boundary the feature asserts; consequences range from controller crash or hang to corruption of driver state that gates the flash protection regions. The fix widens the counters, rejects any request whose word count exceeds both ARRAY_SIZE(FLASHRXBUF) - NPCX_ESPI_FLASH_HEADER_ADDRESS_LEN and NPCX_TAF_RX_PAYLOAD_WORDS (derived from the devicetree rx-plsize), marks such packets with a new invalid_flag so espi_taf_work() answers them with an unsuccessful completion instead of processing them, bounds the transmit payload against FLASHTXBUF, and adds a default case for unsupported cycle types. Only configurations with CONFIG_ESPI_TAF enabled on an NPCX/NPCK target are affected; no in-tree board enables it by default.
Title Out-of-bounds write in the Nuvoton NPCX eSPI Target-Attached-Flash receive path from an unvalidated host-supplied packet length
Weaknesses CWE-787
References
Metrics cvssV3_1

{'score': 6.3, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:H/A:H'}

Subscriptions

Zephyrproject Zephyr
cve-icon MITRE

Status: PUBLISHED

Assigner: zephyr

Published:

Updated: 2026-10-23T21:27:51.509Z

Reserved: 2026-08-22T20:23:02.984Z

Link: CVE-2026-78119

cve-icon Vulnrichment

Updated: 2026-10-23T20:42:58.049Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-21T19:17:03.920

Modified: 2026-10-23T22:17:00.597

Link: CVE-2026-78119

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-22T10:30:04Z

Weaknesses