CVE-2026-74499ALSA: usb-audio: fix OOB write in snd_usbmidi_akai_output()

Official description

In the Linux kernel, the following vulnerability has been resolved: ALSA: usb-audio: fix OOB write in snd_usbmidi_akai_output() snd_usbmidi_akai_output() computes its fill-loop bound buf_end = ep->max_transfer - MAX_AKAI_SYSEX_LEN - 1; as a signed int, so a small device-advertised bulk-OUT max_transfer makes buf_end negative. The loop guard then compares the u32 urb->transfer_buffer_length against that negative int: the usual arithmetic conversion turns buf_end into a large unsigned value, so the guard stays true and each iteration keeps appending SysEx framing and payload bytes past the end of the URB transfer buffer, which is only max_transfer bytes long. A USB device that advertises a tiny bulk-OUT endpoint can therefore trigger an attacker-length- and content-controlled heap out-of-bounds write when a process writes to the created /dev/snd/midiC*D* node. Return early when there is no room for even one SysEx, so the loop is never entered with a bound that would wrap. The loop is the last statement of the function, so bailing out is equivalent to it not running. Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/78dfdeb8d2065524ed5928d6470bf3d3244d1009
• https://git.kernel.org/stable/c/00cc659a42ac4e94ec880fae2c9bf22fce69c2e8
• https://git.kernel.org/stable/c/ce949d66607cfb000b8d8d84f80f35a886e72683
• https://git.kernel.org/stable/c/29a4c29943631301e85f5e9d10f25741bd78e7ba
• https://git.kernel.org/stable/c/9b22a5c8310b0d55d04f5f0159b913a2fb8b444f
• https://git.kernel.org/stable/c/b5305a0d0bb8e90a6fc9f88270d5f6c9b8c40081
• https://git.kernel.org/stable/c/2b7a0f330dd90dd1a7657cec0db019ee1efa4372
• https://git.kernel.org/stable/c/0970274613fb463d376211450cab066d34ebfe6a