CVE-2026-31709
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…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.26%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- EPSS
- 0.26% probability · 18th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-1288
- Affected
- linux/linux kernel
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
References
- https://git.kernel.org/stable/c/0a8cf165566ba55a39fd0f4de172119dd646d39aPatch
- https://git.kernel.org/stable/c/8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12
- https://git.kernel.org/stable/c/b78db9bddc84136f6a0bb49e8883cf200dfb87a8Patch
- https://git.kernel.org/stable/c/b8603d9ae6c9087662b098619996bc4a8064319d
- https://git.kernel.org/stable/c/c2abdebf72000a64603ced84d36ccbd164f11391
- https://git.kernel.org/stable/c/d92f3f0b22414e7515696a02224d0af55e3004a3
- https://git.kernel.org/stable/c/ff0ca46b13b9ef6edbcd238a3b6caacfef8ba0e5
- https://access.redhat.com/errata/RHSA-2026:21556
- https://access.redhat.com/errata/RHSA-2026:21706
- https://access.redhat.com/errata/RHSA-2026:21745
- https://access.redhat.com/errata/RHSA-2026:22900
- https://access.redhat.com/errata/RHSA-2026:22940
- https://access.redhat.com/errata/RHSA-2026:23224
- https://access.redhat.com/errata/RHSA-2026:23237
- https://access.redhat.com/errata/RHSA-2026:23329
- https://access.redhat.com/errata/RHSA-2026:24343
- https://access.redhat.com/security/cve/CVE-2026-31709
- https://bugzilla.redhat.com/show_bug.cgi?id=2464476
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31709.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.