Linux Kernel up to 7.0.1 SMB Client build_sec_desc out-of-bounds

Summaryinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 7.0.1. This impacts the function build_sec_desc of the component SMB Client. The manipulation results in out-of-bounds. This vulnerability is known as CVE-2026-31709. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.0.1. It has been classified as problematic. Affected is the function build_sec_desc of the component SMB Client. The manipulation with an unknown input leads to a out-of-bounds vulnerability. CWE is classifying the issue as CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. This is going to have an impact on confidentiality. CVE summarizes:

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.

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2026-31709 since 03/09/2026. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 318033 (RockyLinux 9 : kernel (RLSA-2026:21556)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 7.0.2 or 7.1-rc1 eliminates this vulnerability. Applying the patch b78db9bddc84136f6a0bb49e8883cf200dfb87a8/0a8cf165566ba55a39fd0f4de172119dd646d39a is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (318033) and CERT Bund (WID-SEC-2026-1346). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• Google Container-Optimized OS
• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• Open Source Linux Kernel
• RESF Rocky Linux
• Microsoft Azure Linux
• Red Hat OpenShift

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.0.0
• 7.0.1

License

• open-source

Website

• Vendor: https://www.kernel.org/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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