CHKDSK in Microsoft Windows 2000 before Update Rollup 1 for SP4, Windows XP, and Windows Server 2003, when running in fix mode, does not properly handle security descriptors if the master file table contains a large number of files or if the descriptors do not satisfy certain NTFS conventions, which could cause ACLs for some files to be reverted to less secure defaults, or cause security descriptors to be removed.