CVE-2025-38527: smb: client: fix use-after-free in cifs_oplock_break

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-08-16 · updated 2026-10-15
Weakness: CWE-416

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.

Affected products

Debian Linux: 11.0
Linux kernel: from 3.16.72 before 3.17; from 4.9.171 before 4.10; from 4.14.114 before 4.15; from 4.19.37 before 4.20; from 5.0.10 before 5.1; from 5.1.1 before 5.15.190 — fixed in 3.17, 4.10, 4.15, 4.20, 5.1, 5.15.190

How to fix

Upgrade to a fixed version: Linux kernel 3.17, 4.10, 4.15, 4.20. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2025-38527 or the next vulnerability affects your stack