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

Summary

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.

Timeline

1. Apr 24, 2026, 2:42 PM UTCCVE published
2. Oct 15, 2026, 1:17 AM UTCRecord last updated

Affected versions

• Linux Linux

  From e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 · fixed in cf2148b880fb7c0fcd727202dbc4fd5d6998b9c2; From e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 · fixed in b5b5d5936a50497fb151c0b122899a6894721c2b; From e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 · fixed in 08f9e6d899b5c834bbcc239eae1bed58d9b15d2c; From e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 · fixed in d2454f4a002d08560a60f214f392e6491cf11560; From e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 · fixed in 46bbcd3ebfb3549c8da1838fc4493e79bd3241e7; From e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 · fixed in 9401f86a224f37b50e6a3ccf1d46a70d5ef8af0a; From e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 · fixed in 53370cf9090777774e07fd9a8ebce67c6cc333ab

• Linux Linux

  5.15

• KernelLinux

  From 5.15.0 · fixed in 6.1.175; From 6.2.0 · fixed in 6.6.136; From 6.7.0 · fixed in 6.12.83; From 6.13.0 · fixed in 6.18.24; From 6.19.0 · fixed in 6.19.14; From 6.20.0 · fixed in 7.0.1

References 7