CVE-2026-93119 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
usb: ljca: bound bank_num in ljca_enumerate_gpio()
ljca_enumerate_gpio() reads desc->bank_num from the device and loops valid_pin[i] = get_unaligned_le32(...) for i < bank_num. valid_pin[]
holds only LJCA_MAX_GPIO_NUM / 32 = 2 entries.
Two checks run before the loop. The reply length must match struct_size(desc, bank_desc, bank_num). The product pins_per_bank * bank_num must not exceed LJCA_MAX_GPIO_NUM. Neither one bounds bank_num against the size of valid_pin[]. The reply is capped at
LJCA_MAX_PAYLOAD_SIZE (60) bytes, so the struct_size check limits bank_num to 9. A device that reports bank_num 9 with pins_per_bank 7 still passes both checks. gpio_num is 63 and the reply is 56 bytes. The loop then writes nine u32 into the two entry array and overruns valid_pin[] on the stack.
A broken or malicious LJCA device can therefore overflow the stack. Reject a bank_num that does not fit valid_pin[].
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel vulnerability identified in the ljca USB driver involves a critical out-of-bounds write caused by insufficient validation of input parameters during GPIO enumeration. The function ljca_enumerate_gpio() is responsible for processing data received from an attached LJCA device, specifically reading bank_num to determine how many banks of GPIO pins are present. This value dictates the number of iterations in a loop that populates the valid_pin array using get_unaligned_le32 operations. However, the valid_pin array is statically sized with only two entries, calculated as LJCA_MAX_GPIO_NUM divided by thirty-two. The existing validation logic checks whether the total reply length matches the expected struct_size and ensures that the product of pins_per_bank and bank_num does not exceed LJCA_MAX_GPIO_NUM. While these checks prevent excessive memory usage in aggregate terms, they fail to constrain bank_num relative to the actual size of the valid_pin array on the stack.
The operational impact stems from a device reporting a high value for bank_num while maintaining a low pins_per_bank count. For instance, if a malicious or broken LJCA device reports bank_num as nine and pins_per_bank as seven, the total pin count is sixty-three, which passes the aggregate check since it does not exceed LJCA_MAX_GPIO_NUM. Additionally, the reply length of fifty-six bytes remains within the LJCA_MAX_PAYLOAD_SIZE limit of sixty bytes. Consequently, both pre-loop validations succeed, allowing execution to proceed into the loop where nine u32 values are written sequentially into valid_pin[]. Since this array only accommodates two entries, five additional writes occur beyond its allocated stack space, resulting in a stack buffer overflow that can corrupt adjacent memory structures and potentially lead to arbitrary code execution or kernel panic.
This vulnerability aligns with CWE-121, which describes a stack-based buffer overflow where data is written past the end of a fixed-size buffer on the call stack. From an offensive security perspective, this flaw facilitates exploitation through malicious hardware interaction, mapping closely to ATT&CK technique T1583, specifically subtechnique T1583.002 for acquiring infrastructure such as compromised or rogue devices that can inject malformed data into a system. The attack vector requires physical access or the ability to connect a custom device via USB, making it a local hardware-based exploitation scenario rather than a remote network exploit.
To mitigate this risk, developers must enforce strict bounds checking on bank_num relative to the size of valid_pin[] before entering the processing loop. Specifically, the validation logic should ensure that bank_num does not exceed LJCA_MAX_GPIO_NUM divided by thirty-two, thereby guaranteeing that all subsequent writes remain within the allocated array boundaries. This fix ensures that even if a device reports high aggregate pin counts with low per-bank values, the iteration count remains constrained to safe limits. Implementing this check prevents stack corruption and maintains kernel integrity when interacting with untrusted USB peripherals.