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Vulnerability record · CVE-2026-31611 · published 24 April 2026

CVE-2026-31611: Linux kernel vulnerability

Linux · Linux Kernel

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.

8.6 CVSS 3.1 High EPSS 0.52% · top 57.9%
8.6CVSS 3.1 base score
0.52%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
7References
17 Jun 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://git.kernel.org/stable/c/08f9e6d899b5c834bbcc239eae1bed58d9b15d2c Patch
https://git.kernel.org/stable/c/46bbcd3ebfb3549c8da1838fc4493e79bd3241e7 Patch
https://git.kernel.org/stable/c/53370cf9090777774e07fd9a8ebce67c6cc333ab Patch
https://git.kernel.org/stable/c/9401f86a224f37b50e6a3ccf1d46a70d5ef8af0a Patch
https://git.kernel.org/stable/c/b5b5d5936a50497fb151c0b122899a6894721c2b Patch
https://git.kernel.org/stable/c/cf2148b880fb7c0fcd727202dbc4fd5d6998b9c2
https://git.kernel.org/stable/c/d2454f4a002d08560a60f214f392e6491cf11560 Patch

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Source: NIST National Vulnerability Database (record CVE-2026-31611), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.