CVE-2026-31611

About vulnerability

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. A flaw was found in the ksmbd component of the Linux kernel. A remote attacker could exploit this vulnerability by sending a specially crafted Access Control Entry (ACE) that causes an out-of-bounds read when parsing security identifiers. This out-of-bounds read can lead to the application of arbitrary, unintended data as a file’s POSIX mode, potentially resulting in incorrect file permissions and unauthorized access to files.

Live-patch status from KernelCare for each operating system.