Detections
Analytics

4.1.10 Ensure discretionary access control permission modification events are collected - chmod/fchmod/fchmodat (32-bit)

Information

Monitor changes to file permissions, attributes, ownership and group. The parameters in this section track changes for system calls that affect file permissions and attributes. The chmod , fchmod and fchmodat system calls affect the permissions associated with a file. The chown , fchown , fchownat and lchown system calls affect owner and group attributes on a file. The setxattr , lsetxattr , fsetxattr (set extended file attributes) and removexattr , lremovexattr , fremovexattr (remove extended file attributes) control extended file attributes. In all cases, an audit record will only be written for non-system user ids (auid >= 1000) and will ignore Daemon events (auid = 4294967295). All audit records will be tagged with the identifier "perm_mod."

Rationale:

Monitoring for changes in file attributes could alert a system administrator to activity that could indicate intruder activity or policy violation.

Solution

For 32 bit systems add the following lines to the /etc/audit/rules.d/audit.rules file:

-a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

For 64 bit systems add the following lines to the /etc/audit/rules.d/audit.rules file:

-a always,exit -F arch=b64 -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b64 -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b64 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

See Also

https://workbench.cisecurity.org/files/2449

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6, CSCv7|5.5

Plugin: Unix

Control ID: eb2a202c6781485942c549f9df642e77c8ca75d161f8d6e399c59f513550dd6c