SMB share permissions
Share-level access is associated with each SMB share and must be reviewed in the context of the server hosting it.
Security risks
File-share access can be broader than it first appears
Windows file-share access may be influenced by SMB permissions, NTFS permissions, local server groups, Active Directory groups, nested membership and single user access directly on the file share. Reviewing only one layer may leave the effective access scope unclear.
Why visibility is difficult
Access information is distributed across the environment
Active Directory contains users, computers and groups, but the permissions granting those identities access to file shares are normally stored on the file servers themselves.
NTFS permissions
Directory and file permissions may differ from the SMB permissions and may change at different levels in the folder structure.
Local server groups
A share or directory may reference a local group whose members include domain users or domain groups.
Nested domain groups
A group intented for a narrow group of users may contain broader groups of users through one or more levels of nesting.
Direct user assignments
Individual accounts may be granted access directly on a share or directory instead of through a purpose-specific group. These entries can be overlooked when access reviews focus mainly on Active Directory group membership.
DFS references
A DFS namespace can present a convenient logical path while the underlying share and file-system permissions remain on another server.
Historical scan data
Older results may no longer reflect current shares, permissions, group membership or server configuration.
Unresolved security identifiers
When an account or group is deleted from Active Directory, an existing permission entry may remain on the share or file system as an unresolved SID. The entry may no longer grant usable access, but it reduces clarity and makes the ACL harder to interpret.
No single complete view
Native Windows tools provide the necessary information in several different places, but there is no single central view that automatically combines share discovery, SMB permissions, NTFS permissions, local groups, nested domain groups and scan context.
Broad access
General access may be granted directly or indirectly
Broad principals such as Everyone,Authenticated Users, Domain Users or a local Users group may be assigned directly to a share or directory.
In other cases, broad access may be introduced indirectly through local-group membership or nested Active Directory groups.
Example: local-group nesting
\\FS02\Finance
NTFS permission:
FS02\Users — Modify
Local group membership:
FS02\Users
└── CONTOSO\Domain UsersThe ACL may appear to reference only a local group, while the resulting access may extend to a much larger part of the domain.
Examples
Conditions that may warrant review
These examples do not by themselves prove that access is inappropriate. They identify conditions that should be checked against policy, ownership and business need.
Broad principal assigned directly
\\FS01\Projects
SMB permission:
Domain Users — ReadIs the share intended for all domain users, or only for a defined project group?
Broad access through nested groups
ACL entry:
CONTOSO\Finance-Readers
Nested membership:
Finance-Readers
└── All-Employees
└── Domain UsersDoes the group name suggest a narrower audience than the effective membership provides?
Direct user assignment
\\FS03\Archive
NTFS permission:
CONTOSO\j.smith — ModifyIs the direct assignment still required, and is its ownership and approval documented?
Direct user permissions
Individual assignments are harder to govern consistently
Individual user accounts are sometimes granted access directly on a share or directory instead of through purpose-specific groups.
Direct assignments may be valid in limited circumstances, but they are harder to review centrally and may remain after job changes, ownership transfers or project completion.
Questions for review
- Why was the user granted access directly?
- Is the access still required?
- Who owns and approved the exception?
- Could a purpose-specific group be used instead?
- Has the assignment been reviewed recently?
- Are any ACL entries shown only as unresolved SIDs?
- Can the original identity and purpose of each entry be established?
- Can obsolete permission entries be removed safely?
Permission hygiene
Deleted identities can leave unresolved SID entries
SMB and NTFS permission entries reference Windows security identifiers. If the corresponding Active Directory account or group is later deleted, the permission entry may remain on the share, directory or file.
Windows may then display the raw SID instead of a recognisable account or group name. This does not normally mean that an unknown active user has gained access, but it creates uncertainty and obscures the current permission structure.
Example: unresolved identity
NTFS permission:
S-1-5-21-123456789-234567890-345678901-1127
Allow — Modify
Account lookup:
Identity could not be resolvedThe entry should be investigated to determine what identity it previously represented, whether the permission is still required and whether it can be removed safely.
Practical testing
Why standard-user scans are valuable
A scan performed with a standard or representative user account provides a practical view of what users with equivalent access can discover and reach.
Representative access
A standard-user scan can show shares and content available through general domain membership, inherited access and nested groups.
Potentially broad exposure
Results may identify locations whose practical audience is wider than the share name, ownership or intended business use suggests.
Authoritative comparison
Administrative or Agent scans can provide a broader or authoritative inventory for comparison with the representative-user result.
What can a user with this access context see and reach?
Interpretation
Observed access must be compared with the share's intended audience
Observed access
The scan shows that the selected credentials can discover or reach the resource.
Potentially broader than intended
The observed access appears wider than the expected audience for the share and warrants review.
Confirm access
The observed access should be compared with the approved or intended access for the share to determine whether it is appropriate.
ShareMon can directly support observation and investigation. Confirming an access mismatch requires comparison with the approved audience, ownership and intended business use of the particular share.
Structured review
Use ShareMon to improve visibility into share access
Discover shares, compare scan contexts and review permission information using evidence collected from the environment.