* [CVE-2026-80824][IMPORTANT] usb: usbfs: fix use-after-free of usb_device in usbdev_release()
@ 2026-09-04 17:31 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-04 17:31 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80824
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: usb: usbfs: fix use-after-free of usb_device in usbdev_release()
Commit: 0a960b88c5979f853019d4dc4957dfbeeb193440
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0a960b88c5979f853019d4dc4957dfbeeb193440
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80824
Analysis date: Fri, 04 Sep 2026 13:31:07 -0400
ActionableScore: 8
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES
Summary:
A deterministic use-after-free in usbfs `usbdev_release()` lets a local user with read/write access to a `/dev/bus/usb` node trigger a kernel crash during mmap-backed async URB cleanup after device disconnect, and the freed object reuse creates a plausible privilege-escalation concern requiring manual review.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80824 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80824
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: IMPORTANT
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-80824 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-80824 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;*CWE-664;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A use after free in usbfs usbdev_release can occur because the usb_device reference is dropped before completed async URBs are drained. When an async URB uses a buffer from the usbfs mmap region, free_async can call dec_usb_memory_use_count and read ps dev bus after the usb_device has already been freed following device disconnect. A local process with read/write access to the relevant /dev/bus/usb node can reach this path through usbfs operations and device removal, causing a kernel crash and creating a plausible UAF based privilege escalation risk. For the CVSS the PR:L is used because the attacker needs a local user context with access to the USB device node, not full administrator privileges. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in the paranoid case may include confidentiality and integrity impact because a freed kernel object is dereferenced and later used as an HCD related pointer.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) YES READ DANGER USB RACE UAF HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=8
ActionableScoreLower=7
## 1. ActionableScore
* Conservative score: 7
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::
## 2. Signal breakdown
Conservative signals:
* Local unprivileged trigger: +1. The commit states this is reachable by an unprivileged process with read/write access to a `/dev/bus/usb` node.
* Generic memory corruption: +2. The failure is an explicit slab use-after-free of `struct usb_device`.
* Real lifetime corruption: +1. `usb_put_dev()` can free the device before `free_async()` finishes using state reachable through `ps->dev`.
* Reliable kernel crash / strong DoS: +1. The report says it reproduces on every attempt and includes a KASAN UAF trace in `dec_usb_memory_use_count()`.
* Weak LPE concern: +1. The freed object is not only read, but a field is used to derive a `struct usb_hcd *` that is later dereferenced. This is a plausible corruption sink, although controlled reclaim or overwrite is not demonstrated.
* Broad/default/common subsystem: +1. usbfs and `/dev/bus/usb` are common on systems with USB device access.
Conservative reduction:
* Requires device disconnect / physical or lifecycle condition: -1. Reliable triggering depends on the USB device being disconnected or otherwise removed while the userspace file/mmap lifetime keeps the release path delayed.
Paranoid adjustment:
* Privilege escalation plausible: +2 instead of weak +1. For the paranoid score, this is a deterministic UAF in a common kernel device path where a freed object field is reused as an HCD-related pointer. That is enough to require manual review for possible LPE even though no controlled reclaim primitive is shown.
## 3. Reachability analysis
A local process can trigger the affected path if it has read/write access to the relevant `/dev/bus/usb` device node. This does not require full root privileges in environments where desktop ACLs, udev rules, USB groups, containers, or service accounts grant USB device access.
The issue is not network reachable. It is tied to local usbfs operations, mmap-backed USB buffers, completed async URB cleanup, and device disconnect/removal timing. The trigger is stronger than a normal race because the description states that a live `MAP_SHARED` VMA keeps the file alive and makes the vulnerable release ordering reproducible.
Namespaces may matter only if USB device nodes are passed into a container. In that case, a container process with access to the host USB device node may be able to reach the same kernel path, so this should not be treated as requiring full host root by default.
## 4. Severity interpretation
This behaves like an Important-class candidate, not an ordinary Moderate cleanup. The core primitive is a real UAF with a demonstrated KASAN trace and reliable reproduction.
Realistic demonstrated impact is local kernel crash / DoS. Theoretical higher impact is plausible because the freed `usb_device` contents are consumed to obtain an HCD-related pointer, but the provided patch does not demonstrate attacker-controlled reclaim, arbitrary write, callback control, or a complete LPE chain. Therefore the conservative score stays below high-end Important, while the paranoid score keeps it in Strong Important candidate territory.
## 5. One-sentence report phrase
A deterministic use-after-free in usbfs `usbdev_release()` lets a local user with read/write access to a `/dev/bus/usb` node trigger a kernel crash during mmap-backed async URB cleanup after device disconnect, and the freed object reuse creates a plausible privilege-escalation concern requiring manual review.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
This is a real and reproducible kernel UAF in a common USB userspace interface, reachable without full administrator privileges in plausible deployments, with at least reliable DoS and a defensible paranoid LPE concern.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: usb: usbfs: fix use-after-free of usb_device in usbdev_release()
Commit: 0a960b88c5979f853019d4dc4957dfbeeb193440
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0a960b88c5979f853019d4dc4957dfbeeb193440
Commit description:
usbdev_release() drops its reference to the struct usb_device before
draining the list of completed async URBs, but that drain path reads back
through the same object: free_async() calls dec_usb_memory_use_count()
for any URB whose buffer came from the usbfs mmap() region, and its first
statement is bus_to_hcd(ps->dev->bus).
After a disconnect the usbfs reference can be the last one, in which case
usb_put_dev() frees the device and the subsequent loop reads offset 80 of
freed memory and uses the result as a struct usb_hcd *, which
hcd_buffer_free_pages() then dereferences.
This is reachable by an unprivileged process that has read/write access to
a /dev/bus/usb node: mmap() the fd, submit one URB with a buffer inside the
mapping, wait for the device to be unplugged, then munmap() and close().
It reproduces on every attempt rather than being a race, because a live
MAP_SHARED vma holds a reference on the struct file, so usbdev_release()
cannot run until the last vma is gone and the freeing branch of
dec_usb_memory_use_count() is always taken.
BUG: KASAN: slab-use-after-free in dec_usb_memory_use_count+0x3ae/0x410
Read of size 8 at addr ffff8880122ee050 by task poc/769
CPU: 1 UID: 1000 PID: 769 Comm: poc Tainted: G B 6.12.94 #3
Call Trace:
dec_usb_memory_use_count+0x3ae/0x410
free_async+0x2aa/0x4f0
usbdev_release+0x375/0x460
__fput+0x3ea/0xb50
__x64_sys_close+0x86/0x100
Allocated by task 11:
usb_alloc_dev+0x55/0xd90
hub_event+0x2524/0x43d0
Freed by task 769:
kfree+0x121/0x360
device_release+0xd2/0x280
usb_put_dev+0x23/0x30
usbdev_release+0x2d8/0x460
Release the device reference after the drain loop instead. Nothing between
the two points requires it to have been dropped.
Fixes: f7d34b4 ("USB: Add support for usbfs zerocopy.")
Cc: [email protected]
Assisted-by: Claude:claude-opus-5
Signed-off-by: Miguel Peñaranda <[email protected]>
Reviewed-by: Alan Stern <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/usb/core/devio.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0a960b88c5979f853019d4dc4957dfbeeb193440
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80824 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80824
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.8
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: 7
Paranoid ActionableScore: 8
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-09-04 17:31 21% [CVE-2026-80824][IMPORTANT] usb: usbfs: fix use-after-free of usb_device in usbdev_release() AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox