Linux: Use After Free
CVE-2026-64396 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. The record lists versions 367c42a611fe488b7b03f1f6737f4dee0e8b20a2, 7703fd9aba1f2483c8e55f9ff73b7663e0761ed9, 463bbd79698513af4dad50fe1c573825f297ca2e as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.43% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 367c42a611fe488b7b03f1f6737f4dee0e8b20a2 or 7703fd9aba1f2483c8e55f9ff73b7663e0761ed9 or 463bbd79698513af4dad50fe1c573825f297ca2e or 5aa1cb01155f96824003baf7997cdf1f150caba3, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.1.178 or 6.6.145 or 6.12.96 or 6.18.39, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 367c42a611fe488b7b03f1f6737f4dee0e8b20a2; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 7703fd9aba1f2483c8e55f9ff73b7663e0761ed9; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 463bbd79698513af4dad50fe1c573825f297ca2e; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 5aa1cb01155f96824003baf7997cdf1f150caba3; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 5c75275c0fc9a2deb0d8f5604edcb16f288171c8; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, d20d1c8ba5765d1d12eefc0aee6385ab3f240e1e; 5.15 | 367c42a611fe488b7b03f1f6737f4dee0e8b20a2, 7703fd9aba1f2483c8e55f9ff73b7663e0761ed9, 463bbd79698513af4dad50fe1c573825f297ca2e, 5aa1cb01155f96824003baf7997cdf1f150caba3, 5c75275c0fc9a2deb0d8f5604edcb16f288171c8, d20d1c8ba5765d1d12eefc0aee6385ab3f240e1e |
| Linux | Linux Kernel | 5.15 up to, but not including, 6.1.178; 6.2 up to, but not including, 6.6.145; 6.7 up to, but not including, 6.12.96; 6.13 up to, but not including, 6.18.39; 6.19 up to, but not including, 7.1.4 | 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.
Official description
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().
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/367c42a611fe488b7b03f1f6737f4dee0e8b20a2
- git.kernel.org/stable/c/463bbd79698513af4dad50fe1c573825f297ca2e
- git.kernel.org/stable/c/5aa1cb01155f96824003baf7997cdf1f150caba3
- git.kernel.org/stable/c/5c75275c0fc9a2deb0d8f5604edcb16f288171c8
- git.kernel.org/stable/c/7703fd9aba1f2483c8e55f9ff73b7663e0761ed9
- git.kernel.org/stable/c/d20d1c8ba5765d1d12eefc0aee6385ab3f240e1e
Recent Use After Free vulnerabilities
- 9.8 Critical severity
- 7.8 High severity
- 8.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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