CVE-2026-63896
Low risk· EPSS 10%Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
In the Linux kernel, a vulnerability in the USB gadget composite driver's WebUSB GET_URL handler causes an integer underflow. When the host supplies a wLength smaller than the URL descriptor header, the unsigned subtraction wraps, leading to a massive out-of-bounds memory copy (nearly 4 GB).
Risk Assessment
An attacker with USB access can send a single SETUP packet to a vulnerable gadget (with webusb enabled and a landingPage configured), triggering a buffer overflow that may crash the system or allow arbitrary code execution.
Recommendation
Immediately update the Linux kernel to a version containing the fix, which adds a check for small wLength before performing arithmetic operations.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: usb: gadget: composite: fix integer underflow in WebUSB GET_URL handling The WebUSB GET_URL handler in composite_setup() narrows landing_page_length to fit the host-supplied wLength using landing_page_length = w_length - WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + landing_page_offset; If wLength is smaller than WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH the unsigned subtraction wraps, and the subsequent memcpy(url_descriptor->URL, cdev->landing_page + landing_page_offset, landing_page_length - landing_page_offset); ends up copying close to UINT_MAX bytes from cdev->landing_page into cdev->req->buf. KASAN reports a slab-out-of-bounds in composite_setup on the kmalloc-2k gadget_info allocation, and FORTIFY_SOURCE traps the memcpy as a 4294967293-byte field-spanning write into url_descriptor->URL (size 252). A USB host can reach this from a single SETUP packet against any gadget that has webusb/use=1 and a landingPage configured. Handle the small-wLength case before the math: when the host requested fewer bytes than the URL descriptor header, only the header is meaningful and no URL bytes need to be copied. Setting landing_page_length to landing_page_offset makes the existing memcpy a no-op and leaves the descriptor returned to the host unchanged for all larger wLength values.