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Linux KernelOperating system · Linux

CVE-2025-38523

MEDIUM · 5.5 CVSS v3.1 Published 2025-08-16
Fix available
A fix is available. Upgrade to 6.12.36 / 6.15.8 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: cifs: Fix the smbd_response slab to allow usercopy The handling of received data in the smbdirect client code involves using copy_to_iter() to copy data from the smbd_reponse struct's packet trailer to a folioq buffer provided by netfslib that encapsulates a chunk of pagecache. If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks then performed in copy_to_iter() oopsing with something like the following: CIFS: Attempting to mount //172.31.9.1/test CIFS: VFS: RDMA transport established usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)! ------------[ cut here ]------------ kernel BUG at mm/usercopy.c:102! ... RIP: 0010:usercopy_abort+0x6c/0x80 ... Call Trace: <TASK> __check_heap_object+0xe3/0x120 __check_object_size+0x4dc/0x6d0 smbd_recv+0x77f/0xfe0 [cifs] cifs_readv_from_socket+0x276/0x8f0 [cifs] cifs_read_from_socket+0xcd/0x120 [cifs] cifs_demultiplex_thread+0x7e9/0x2d50 [cifs] kthread+0x396/0x830 ret_from_fork+0x2b8/0x3b0 ret_from_fork_asm+0x1a/0x30 The problem is that the smbd_response slab's packet field isn't marked as being permitted for usercopy. Fix this by passing parameters to kmem_slab_create() to indicate that copy_to_iter() is permitted from the packet region of the smbd_response slab objects, less the header space.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 6.12, < 6.12.36>= 6.13, < 6.15.8= 6.16

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.12.36 / 6.15.8 or later
Fixed in 6.12.366.15.8
Vendor patch git.kernel.org →
Recommended fix High confidence

6.12.36+, 6.15.8+, or 6.16.1+ (depending on base version)

  1. 1. Identify the currently running Linux kernel version using `uname -r` or `cat /proc/version`
  2. 2. Check if the kernel version is one of the affected versions: >= 6.12 and < 6.12.36, >= 6.13 and < 6.15.8, or exactly 6.16
  3. 3. If affected, upgrade the kernel to a patched stable version: 6.12.36 or later for 6.12.x kernels, 6.15.8 or later for 6.13.x/6.14.x kernels, or 6.16.1/6.16.2 or later for 6.16 kernels
  4. 4. Update the boot loader configuration (e.g., update-grub for GRUB) to ensure the new kernel will be used after reboot
  5. 5. Reboot the system to load the patched kernel
  6. 6. Verify the fix is applied by checking the kernel version (`uname -r`) and confirming the CIFS smbdirect functionality works correctly without usercopy errors
  7. 7. If immediate upgrade is not possible, disable SMB Direct (RDMA) functionality in CIFS mount options as a temporary mitigation
Caveat Kernel upgrades may require system reboot and could introduce compatibility issues with out-of-tree kernel modules or specific hardware drivers; always test in staging first

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

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