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Linux KernelOperating system · Linux

CVE-2025-38527

HIGH · 7.8 CVSS v3.1 Published 2025-08-16
Fix available
A fix is available. Upgrade to 3.17 / 4.10 or later.
See remediation →
80/100
Remediation priority · High
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: smb: client: fix use-after-free in cifs_oplock_break A race condition can occur in cifs_oplock_break() leading to a use-after-free of the cinode structure when unmounting: cifs_oplock_break() _cifsFileInfo_put(cfile) cifsFileInfo_put_final() cifs_sb_deactive() [last ref, start releasing sb] kill_sb() kill_anon_super() generic_shutdown_super() evict_inodes() dispose_list() evict() destroy_inode() call_rcu(&inode->i_rcu, i_callback) spin_lock(&cinode->open_file_lock) <- OK [later] i_callback() cifs_free_inode() kmem_cache_free(cinode) spin_unlock(&cinode->open_file_lock) <- UAF cifs_done_oplock_break(cinode) <- UAF The issue occurs when umount has already released its reference to the superblock. When _cifsFileInfo_put() calls cifs_sb_deactive(), this releases the last reference, triggering the immediate cleanup of all inodes under RCU. However, cifs_oplock_break() continues to access the cinode after this point, resulting in use-after-free. Fix this by holding an extra reference to the superblock during the entire oplock break operation. This ensures that the superblock and its inodes remain valid until the oplock break completes.

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
How this class of weakness works · CWE-416

Memory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.

General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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:>= 3.16.72, < 3.17>= 4.9.171, < 4.10>= 4.14.114, < 4.15>= 4.19.37, < 4.20>= 5.0.10, < 5.1>= 5.1.1, < 5.15.190>= 5.16, < 6.1.147>= 6.2, < 6.6.100>= 6.7, < 6.12.40>= 6.13, < 6.15.8= 5.1= 6.16
Debian LinuxOperating system
Affected:= 11.0

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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 3.17 / 4.10 / 4.15 or later
Fixed in 3.174.104.15
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux Kernel 3.17, 4.10, 4.15, or 4.20 (depending on your affected branch); or Debian 11 kernel update

  1. Obtain the kernel source code for your affected version (3.16.x, 4.9.x, 4.14.x, or 4.19.x)
  2. Apply the patch from commit 09bce2138a30ef10d8821c8c3f73a4ab7a5726bc: https://git.kernel.org/stable/c/09bce2138a30ef10d8821c8c3f73a4ab7a5726bc
  3. The patch adds an extra superblock reference in cifs_oplock_break() to prevent the cinode from being freed prematurely during unmount
  4. Recompile the kernel with the fix applied
  5. Reboot into the patched kernel
  6. For Debian 11 (bullseye), apply the equivalent Debian kernel security update once available via apt-get update && apt-get upgrade
Caveat None expected - this is a bug fix for a race condition; the fix adds reference counting to prevent use-after-free

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 $3,200. 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

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-38527 in production — separate from our analysis above.

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