Detections
Analytics
4.1.10 Ensure discretionary access control permission modification events are collected - chmod fchmod fchmodat x64
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/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/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
Impact:
Auditing can produce a large amount of information, creating large and/or many audit log files.
Notes:
Reloading the auditd config to set active settings may require a system reboot.
See Also
Item Details
Audit Name: CIS Debian 9 Workstation L2 v1.0.1
Category: CONFIGURATION MANAGEMENT
References: 800-53|CM-6, CSCv7|5.5
Plugin: Unix
Control ID: 57e94526ec3f2c8a3a652ead4dd5f1851065c501c3eac43e907fe7b9b12b169e