CyberSecBulletin
CVE-2025-38527NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2025-38527 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 4256a483fe58af66a46cbf3dc48ff26e580d3308, 0a4eec84d4d2c4085d4ed8630fd74e4b39033c1b, 2baaf5bbab2ac474c4f92c10fcb3310f824db995 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 0.46% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 4256a483fe58af66a46cbf3dc48ff26e580d3308 or 0a4eec84d4d2c4085d4ed8630fd74e4b39033c1b or 2baaf5bbab2ac474c4f92c10fcb3310f824db995 or 09bce2138a30ef10d8821c8c3f73a4ab7a5726bc, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 3.17 or 4.10 or 4.15 or 4.20, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxb98749cac4a695f084a5ff076f4510b23e353ecd up to, but not including, 4256a483fe58af66a46cbf3dc48ff26e580d3308; b98749cac4a695f084a5ff076f4510b23e353ecd up to, but not including, 0a4eec84d4d2c4085d4ed8630fd74e4b39033c1b; b98749cac4a695f084a5ff076f4510b23e353ecd up to, but not including, 2baaf5bbab2ac474c4f92c10fcb3310f824db995; b98749cac4a695f084a5ff076f4510b23e353ecd up to, but not including, 09bce2138a30ef10d8821c8c3f73a4ab7a5726bc; b98749cac4a695f084a5ff076f4510b23e353ecd up to, but not including, da11bd4b697b393a207f19a2ed7d382a811a3ddc; b98749cac4a695f084a5ff076f4510b23e353ecd up to, but not including, 705c79101ccf9edea5a00d761491a03ced314210; 2429fcf06d3cb962693868ab0a927c9038f12a2d; 1ee4f2d7cdcd4508cc3cbe3b2622d7177b89da12; and 9 more ranges4256a483fe58af66a46cbf3dc48ff26e580d3308, 0a4eec84d4d2c4085d4ed8630fd74e4b39033c1b, 2baaf5bbab2ac474c4f92c10fcb3310f824db995, 09bce2138a30ef10d8821c8c3f73a4ab7a5726bc, da11bd4b697b393a207f19a2ed7d382a811a3ddc, 705c79101ccf9edea5a00d761491a03ced314210
LinuxLinux Kernel3.16.72 up to, but not including, 3.17; 4.9.171 up to, but not including, 4.10; 4.14.114 up to, but not including, 4.15; 4.19.37 up to, but not including, 4.20; 5.0.10 up to, but not including, 5.1; 5.1.1 up to, but not including, 5.15.190; 5.16 up to, but not including, 6.1.147; 6.2 up to, but not including, 6.6.100; and 4 more ranges3.17, 4.10, 4.15, 4.20, 5.1, 5.15.190
DebianDebian Linux11.0Not stated

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
LocalThe attacker needs local access or must trick a user into running something.
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:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.19.8CriticalCNA
CVSS 3.17.8HighNVD

Official description

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.

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.

More Use After Free vulnerabilities (CWE-416)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Recent Use After Free vulnerabilities

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