Bug 2507037 (CVE-2026-64396) - CVE-2026-64396 kernel: ksmbd: Use-after-free vulnerability allows arbitrary code execution or denial of service
Summary: CVE-2026-64396 kernel: ksmbd: Use-after-free vulnerability allows arbitrary c...
Keywords:
Status: NEW
Alias: CVE-2026-64396
Product: Security Response
Classification: Other
Component: vulnerability-draft
Version: unspecified
Hardware: All
OS: Linux
high
high
Target Milestone: ---
Assignee: Product Security DevOps Team
QA Contact:
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Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-07-25 10:01 UTC by OSIDB Bzimport
Modified: 2026-08-13 15:04 UTC (History)
2 users (show)

Fixed In Version:
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Description OSIDB Bzimport 2026-07-25 10:01:44 UTC
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix UAF of struct file_lock in SMB2_LOCK deferred-lock cancellation

When a blocking byte-range lock request is deferred in the
FILE_LOCK_DEFERRED path, ksmbd registers the asynchronous work into
the connection's async_requests list via setup_async_work(). The cancel
callback smb2_remove_blocked_lock() holds a reference to the flock.

If the lock waiter is subsequently woken up but the work state is no
longer KSMBD_WORK_ACTIVE (e.g., due to a concurrent cancellation), the
cleanup path calls locks_free_lock(flock) without dequeuing the work from
the async_requests list. Concurrently, smb2_cancel() walks the list
under conn->request_lock and invokes the cancel callback, which then
dereferences the already freed 'flock'. This leads to a slab-use-after-free
inside __wake_up_common.

Fix this by restructuring the cleanup logic after the worker returns
from ksmbd_vfs_posix_lock_wait(). Move list_del(&smb_lock->llist) and
release_async_work(work) to the top of the cleanup block. This guarantees
that the async work is completely dequeued and serialized under
conn->request_lock before locks_free_lock(flock) is called, rendering
the flock unreachable for any concurrent smb2_cancel().

Comment 1 Mauro Matteo Cascella 2026-07-28 16:10:33 UTC
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026072528-CVE-2026-64396-7ca2@gregkh/T


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