CVE-2026-80975
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel, a vulnerability exists in the mfd: qnap-mcu driver. The qnap_mcu_exec() function publishes an on-stack buffer (rx) to the receive path, which can write to it after a command timeout or write failure when the stack frame is no longer valid. This leads to stack memory corruption and potential arbitrary code execution.
Risk Assessment
The vulnerability can cause kernel memory corruption, system crash, or privilege escalation by a local attacker. In environments with access to the QNAP MCU device, the risk is high.
Recommendation
Update the Linux kernel to a version containing the fix that moves the receive buffer into the qnap_mcu structure. If updating is not possible, restrict access to devices using this driver.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: mfd: qnap-mcu: keep the reply buffer alive past a command timeout qnap_mcu_exec() publishes an on-stack buffer to the receive path: unsigned char rx[QNAP_MCU_RX_BUFFER_SIZE]; ... reply->data = rx; reply->length = length; and qnap_mcu_receive_buf() writes into it from the serdev receive path, which runs out of flush_to_ldisc() and is not serialized against qnap_mcu_exec() at all. bus_lock cannot cover it, because qnap_mcu_exec() holds that mutex across wait_for_completion_timeout(). On a timeout qnap_mcu_exec() returns with reply->data still pointing at its own frame. A reply that arrives late, or an unsolicited message from the MCU, is then written into a stack frame that has been left, corrupting whatever runs next on that stack. The same applies when qnap_mcu_write() fails, since that path returns without touching the reply state either. Move the receive buffer into struct qnap_mcu. It is 37 bytes and the structure is devm_kzalloc()ed, so it lives as long as the driver, and a late write lands in memory that is still valid and is reinitialized by the next command. bus_lock keeps commands from sharing it. This deliberately does not clear reply->data or reply->length on the timeout path. Doing so races with qnap_mcu_receive_buf(), which reads both after its if (!reply->length) return size; check: clearing reply->data gives a NULL dereference, and clearing reply->length alone removes the reply->received == reply->length exit condition, so the copy loop runs until the uart chunk is consumed and overruns the buffer. Leaving both set keeps the write bounded by reply->length, which qnap_mcu_exec() has already checked against sizeof(mcu->rx).
Vulnerability data from NVD (NIST) · CISA KEV · EPSS