CVE-2026-63896
Received Received - Intake

Integer Underflow in Linux Kernel USB Gadget Composite Driver

Publication date: 2026-07-19

Last updated on: 2026-07-19

Assigner: kernel.org

Description
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.

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Meta Information

Published
2026-07-19
Last Modified
2026-07-19
Generated
2026-07-20
AI Q&A
2026-07-19
EPSS Evaluated
N/A
NVD
CVE-2026-63896
EUVD
EUVD-2026-45669

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux_kernel linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability is an integer underflow in the Linux kernel's WebUSB GET_URL handling. When a USB host sends a small wLength value in a SETUP packet, the code incorrectly calculates the length to copy, leading to a very large memcpy operation that overflows a buffer. This can cause memory corruption or crashes.

Detection Guidance

This vulnerability is specific to the Linux kernel's USB gadget composite driver and requires a USB host to trigger it. Detection would involve checking kernel logs for slab-out-of-bounds errors or FORTIFY_SOURCE warnings related to composite_setup() in the USB gadget subsystem. No direct network detection commands are applicable.

Impact Analysis

If exploited, this flaw could allow a malicious USB host to crash the system or execute arbitrary code by sending a specially crafted SETUP packet to a vulnerable USB gadget with WebUSB enabled. It may also cause denial-of-service conditions.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards. It is a low-level kernel memory corruption issue in USB gadget handling that could lead to denial of service or potential data corruption in a USB device context. Compliance impacts would only occur if this flaw enabled unauthorized data access or disruption in systems handling regulated data.

Mitigation Strategies

Apply the Linux kernel patch that fixes the integer underflow in the WebUSB GET_URL handler. If patching is not immediately possible, disable USB gadget functionality with webusb/use=1 or remove the landingPage configuration to prevent the vulnerable code path from being triggered.

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