high CVSS 8.8 EPSS 0.63%

CVE-2026-64396·Kernel vulnerability

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().

Severity
high
Software
Kernel
Fixed in
7.1.4
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.63% — higher than 49% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-64396 scores 8.8 on CVSS, so a successful attack would be serious — but at 0.63%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

From: 6.19

Until: 7.1.4

Fixed in: 7.1.4

How to fix this CVE

Update your Linux kernel to version 7.1.4 or later to patch a use-after-free vulnerability in the ksmbd SMB2 locking mechanism. This vulnerability affects systems running kernel versions 6.19 through 7.1.3 and requires immediate kernel patching to prevent potential memory corruption during concurrent file lock cancellations.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Check your kernel version: uname -r — compare the version number against 6.19 to 7.1.3 to determine if you are in the affected range
  2. Verify ksmbd is loaded in your kernel: lsmod | grep ksmbd — if it returns no output, the vulnerable component is not active
  3. Search system logs for kernel panic or UAF-related errors: grep -i 'use-after-free\|UAF\|slab-use-after-free' /var/log/kern.log /var/log/syslog
  4. After patching, reboot the system and verify the new kernel is active: uname -r — confirm the version is 7.1.4 or higher

FAQ

What is CVE-2026-64396?

This is a use-after-free vulnerability in the Linux kernel's ksmbd SMB2 file locking implementation that occurs when concurrent deferred lock cancellations attempt to access memory that has already been freed, potentially causing kernel memory corruption.

Is CVE-2026-64396 being actively exploited?

No, CVE-2026-64396 is not listed on the CISA Known Exploited Vulnerabilities catalog and no public exploits are currently available.

What versions of Kernel are affected by CVE-2026-64396?

Linux kernel versions 6.19 through 7.1.3 are vulnerable; kernel 7.1.4 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-64396?

Run 'uname -r' to get your kernel version; if it reports a version between 6.19 and 7.1.3, your system is vulnerable and requires updating.

Does Defensia detect CVE-2026-64396?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2026-64396 will appear in your dashboard with remediation steps.

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References

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