Linux Kernel ksmbd SMB server Vulnerability Rated 8.6 CVSS

Last refreshed2026-10-15

Status: UPDATED | Advisory ID: CVE-2026-31611

Key Details

CVE	CVE-2026-31611
CVSS Score / Version	8.6 (High) / CVSS v3.1
Updated	2026-10-15
CVSS Vector	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H`
CVSS Prose	attack vector is network; attack complexity is low; privileges required is none; user interaction is none; scope is unchanged; confidentiality impact is low; integrity impact is low; availability impact is high.
Affected products	Linux Kernel and Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
Exploitation prediction (EPSS)	0.54% probability of exploitation in the next 30 days (44% percentile) -- FIRST.org's EPSS model.

Vendor	Product	Affected Versions	Patch Status
Linux	Linux Kernel
Siemens	SIMATIC S7-1500 TM MFP - GNU/Linux subsystem

Vendor

Product

Affected Versions

Patch Status

Linux

Linux Kernel

Siemens

SIMATIC S7-1500 TM MFP - GNU/Linux subsystem

Subsystems	Controllers & Field I/O, OT Supporting Infrastructure
Sectors	All Sectors

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

ksmbd: require 3 sub-authorities before reading sub_auth[2]

parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on

match reads sid.sub_auth[2] as the file mode. If sid_unix_NFS_mode is

the prefix S-1-5-88-3 with num_subauth = 2 then compare_sids() compares

only min(num_subauth, 2) sub-authorities so a client SID with

num_subauth = 2 and sub_auth = {88, 3} will match.

If num_subauth = 2 and the ACE is placed at the very end of the security

descriptor, sub_auth[2] will be 4 bytes past end_of_acl. The

out-of-band bytes will then be masked to the low 9 bits and applied as

the file's POSIX mode, probably not something that is good to have

happen.

Fix this up by forcing the SID to actually carry a third sub-authority

before reading it at all. (NVD)

Monitor Linux's and Siemens's web pages for any future patch releases.

Source	Reference
NVD	https://nvd.nist.gov/vuln/detail/CVE-2026-31611
CVE	https://www.cve.org/CVERecord?id=CVE-2026-31611

Source

Reference

NVD

CVE