CVE-2026-68370

Received Received - Intake

Race Condition in Linux Kernel USB Gadget Subsystem Leads to Use-After-Free

Publication date: 2026-08-10

Last updated on: 2026-08-19

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: dummy_hcd: prevent fifo_req reuse during giveback dummy_hcd embeds a single shared usb_request (dum->fifo_req) that the "emulated single-request FIFO" fast-path in dummy_queue() reuses for small IN transfers: it copies the caller's request into it (req->req = *_req) and queues it, treating list_empty(&fifo_req.queue) as "the slot is free". The completion side (dummy_timer/transfer/nuke/dummy_dequeue) follows the standard pattern: list_del_init(&req->queue) unlinks the request, then the lock is dropped and usb_gadget_giveback_request() invokes req->complete(). But list_del_init() makes fifo_req.queue look empty *before* the completion callback returns, so a concurrent dummy_queue() on another CPU sees the slot as free, reuses fifo_req and runs req->req = *_req -- overwriting req->complete while dummy_timer is mid-calling it. The indirect call then jumps to a clobbered pointer, causing a general protection fault / page fault in dummy_timer (syzkaller extid faf3a6cf579fc65591ca). The clobbering write is an in-bounds memcpy on a live shared object, so KASAN cannot flag it. Add a fifo_req_busy bit covering the shared request's whole lifetime: set it in dummy_queue() when the FIFO fast-path takes fifo_req (making it the fast-path guard, replacing the list_empty(&fifo_req.queue) test), and clear it after the completion callback has returned, via a dummy_giveback() helper used at all four gadget-request giveback sites. The shared slot can no longer be reused until its completion callback has finished.

CVSS Scores

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Meta Information

Published

2026-08-10

Last Modified

2026-08-19

Generated

2026-08-30

AI Q&A

2026-08-10

EPSS Evaluated

2026-08-29

NVD

CVE-2026-68370

EUVD

EUVD-2026-55471

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This is a race condition in the Linux kernel's USB gadget dummy_hcd driver. It involves a shared USB request (fifo_req) that is reused during small data transfers. A concurrency issue allows the request to be overwritten while its completion callback is still executing, leading to a corrupted function pointer and a kernel crash.

Detection Guidance

This vulnerability is specific to the Linux kernel's USB gadget subsystem and requires kernel-level detection. There are no direct network commands to detect it. Monitor kernel logs for general protection faults or page faults in the USB gadget code, particularly during USB device operations. Check for crashes in dummy_hcd or related modules.

Impact Analysis

If exploited, this vulnerability can cause a kernel crash (general protection fault or page fault) on affected systems. This may lead to denial-of-service conditions, system instability, or potential unauthorized access if combined with other exploits. Systems using the dummy_hcd driver are at risk.

Compliance Impact

This vulnerability does not directly affect compliance with standards like GDPR or HIPAA as it is a low-level kernel issue related to memory corruption in the Linux USB gadget subsystem. Compliance impacts would only occur if this flaw led to data breaches or unauthorized access, which is not described in the provided context.

Mitigation Strategies

Apply the Linux kernel patch that resolves this issue. Update to a kernel version containing the fix for CVE-2026-68370. If patching is not immediately possible, disable the dummy_hcd module if unused to reduce attack surface.

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