CVE-2026-31709

Summary

In the Linux kernel, the following vulnerability has been resolved:

smb: client: validate the whole DACL before rewriting it in cifsacl

build_sec_desc() and id_mode_to_cifs_acl() derive a DACL pointer from a server-supplied dacloffset and then use the incoming ACL to rebuild the chmod/chown security descriptor.

The original fix only checked that the struct smb_acl header fits before reading dacl_ptr->size or dacl_ptr->num_aces. That avoids the immediate header-field OOB read, but the rewrite helpers still walk ACEs based on pdacl->num_aces with no structural validation of the incoming DACL body.

A malicious server can return a truncated DACL that still contains a header, claims one or more ACEs, and then drive replace_sids_and_copy_aces() or set_chmod_dacl() past the validated extent while they compare or copy attacker-controlled ACEs.

Factor the DACL structural checks into validate_dacl(), extend them to validate each ACE against the DACL bounds, and use the shared validator before the chmod/chown rebuild paths. parse_dacl() reuses the same validator so the read-side parser and write-side rewrite paths agree on what constitutes a well-formed incoming DACL.

Affected Software

VendorProductVersion RangeStatus
LinuxLinuxbc3e9dd9d104ca1b75644eab87b38ce8a924aef4 < b8603d9ae6c9087662b098619996bc4a8064319daffected
LinuxLinuxbc3e9dd9d104ca1b75644eab87b38ce8a924aef4 < c2abdebf72000a64603ced84d36ccbd164f11391affected
LinuxLinuxbc3e9dd9d104ca1b75644eab87b38ce8a924aef4 < 8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12affected
LinuxLinuxbc3e9dd9d104ca1b75644eab87b38ce8a924aef4 < d92f3f0b22414e7515696a02224d0af55e3004a3affected
LinuxLinuxbc3e9dd9d104ca1b75644eab87b38ce8a924aef4 < ff0ca46b13b9ef6edbcd238a3b6caacfef8ba0e5affected
LinuxLinuxbc3e9dd9d104ca1b75644eab87b38ce8a924aef4 < b78db9bddc84136f6a0bb49e8883cf200dfb87a8affected
LinuxLinuxbc3e9dd9d104ca1b75644eab87b38ce8a924aef4 < 0a8cf165566ba55a39fd0f4de172119dd646d39aaffected
LinuxLinux5.12affected
LinuxLinux0 < 5.12unaffected
LinuxLinux5.15.210 <= 5.15.*unaffected
LinuxLinux6.1.176 <= 6.1.*unaffected
LinuxLinux6.6.140 <= 6.6.*unaffected
LinuxLinux6.12.86 <= 6.12.*unaffected
LinuxLinux6.18.35 <= 6.18.*unaffected
LinuxLinux7.0.2 <= 7.0.*unaffected
LinuxLinux7.1 <= *unaffected

Weaknesses

ADP Enrichment

kernel: smb: client: validate the whole DACL before rewriting it in cifsacl

Additional References

References