CVE-2026-63903: USB: serial: belkin_sa: validate interrupt status length
In the Linux kernel, the following vulnerability has been resolved:
USB: serial: belkinsa: validate interrupt status length
The Belkin interrupt callback treats interrupt data as a four-byte status report and reads LSR/MSR fields at offsets 2 and 3. The interrupt-in buffer length is derived from endpoint wMaxPacketSize, and short interrupt transfers may complete successfully with a smaller actuallength.
Check the completed interrupt packet length before parsing status fields so short interrupt endpoints and short successful packets are ignored instead of causing out-of-bounds or stale status-byte reads.
KASAN report as below:
BUG: KASAN: slab-out-of-bounds in belkinsareadintcallback() Read of size 1 Call trace: belkinsareadintcallback() (drivers/usb/serial/belkinsa.c:202) usbhcdgivebackurb() (drivers/usb/core/hcd.c:1630) dummytimer() (?:?)
Affected Software
Remediation
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In the Belkin USB serial interrupt callback, validate that the completed interrupt packet actual_length is at least 4 before parsing status fields at offsets 2 and 3; ignore short interrupt endpoints and short successful packets.
Event History
Frequently Asked Questions
What level of access does an attacker need?
The severity vector indicates local attack access, low privileges required, and no user interaction required. It also indicates high confidentiality and availability impact, with no integrity impact.
Which systems are exposed?
Affected software listings include the Linux kernel and Ubuntu kernel packages for standard, FIPS, AWS, Azure, and GCP variants. The vulnerable code is in the Belkin USB serial driver and is reached through its interrupt callback.
What condition triggers the unsafe read?
The callback expects a four-byte interrupt status report and reads bytes at offsets 2 and 3. A short successful interrupt transfer, or an interrupt endpoint with a smaller packet size, can leave the completed packet too short for those reads.
How can an existing issue be identified?
Kernel AddressSanitizer may report a slab-out-of-bounds read in belkin_sa_read_int_callback(), with the USB completion path including __usb_hcd_giveback_urb(). The report describes a one-byte read at drivers/usb/serial/belkin_sa.c:202.