Cis Ubuntu2004 V300 6 3 3 7

---
name: cis-ubuntu2004-v300-6-3-3-7
description: "Ensure unsuccessful file access attempts are collected"
category: cis-logging
version: "3.0.0"
author: cyberstrike-official
tags: [cis, ubuntu, linux, ubuntu-20.04, auditing, auditd]
cis_id: "6.3.3.7"
cis_benchmark: "CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0"
tech_stack: [ubuntu, linux]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# 6.3.3.7 Ensure unsuccessful file access attempts are collected (Automated)

## Profile

- Level 2 - Server
- Level 2 - Workstation

## Description

Monitor for unsuccessful attempts to access files. The following parameters are associated with system calls that control files:

- creation - `creat`
- opening - `open`, `openat`
- truncation - `truncate`, `ftruncate`

An audit log record will only be written if all of the following criteria is met for the user when trying to access a file:

- a non-privileged user (auid>=UID_MIN)
- is not a Daemon event (auid=4294967295/unset/-1)
- if the system call returned EACCES (permission denied) or EPERM (some other permanent error associated with the specific system call)

## Rationale

Failed attempts to open, create or truncate files could be an indication that an individual or process is trying to gain unauthorized access to the system.

## Audit Procedure

### Command Line

On disk configuration - Run the following command to check the on disk rules:

```bash
# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && awk "/^ *-a *always,exit/ \
&&/ -F *arch=b(32|64)/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -F *auid>=${UID_MIN}/ \
&&(/ -F *exit=-EACCES/||/ -F *exit=-EPERM/) \
&&/ -S/ \
&&/creat/ \
&&/open/ \
&&/truncate/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" /etc/audit/rules.d/*.rules \
|| printf "ERROR: Variable 'UID_MIN' is unset.\n"
}
```

Verify the output includes:

```
-a always,exit -F arch=b64 -S creat,open,openat,truncate,ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -k access
-a always,exit -F arch=b64 -S creat,open,openat,truncate,ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -k access
-a always,exit -F arch=b32 -S creat,open,openat,truncate,ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -k access
-a always,exit -F arch=b32 -S creat,open,openat,truncate,ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -k access
```

## Expected Result

Both on disk and running configuration should show file access attempt audit rules.

## Remediation

### Command Line

Create audit rules - Edit or create a file in the `/etc/audit/rules.d/` directory, ending in `.rules` extension, with the relevant rules to monitor unsuccessful file access attempts.

Example:

```bash
# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && printf "
-a always,exit -F arch=b64 -S creat,open,openat,truncate,ftruncate -F exit=-EACCES -F auid>=${UID_MIN} -F auid!=unset -k access
-a always,exit -F arch=b64 -S creat,open,openat,truncate,ftruncate -F exit=-EPERM -F auid>=${UID_MIN} -F auid!=unset -k access
-a always,exit -F arch=b32 -S creat,open,openat,truncate,ftruncate -F exit=-EACCES -F auid>=${UID_MIN} -F auid!=unset -k access
-a always,exit -F arch=b32 -S creat,open,openat,truncate,ftruncate -F exit=-EPERM -F auid>=${UID_MIN} -F auid!=unset -k access
" >> /etc/audit/rules.d/50-access.rules || printf "ERROR: Variable 'UID_MIN' is unset.\n"
}
```

Load audit rules - Merge and load the rules into active configuration:

```bash
# augenrules --load
```

Check if reboot is required:

```bash
# if [[ $(auditctl -s | grep "enabled") =~ "2" ]]; then printf "Reboot required to load rules\n"; fi
```

## References

1. NIST SP 800-53 Rev. 5: AU-3

## CIS Controls

| Controls Version | Control                                                             | IG 1 | IG 2 | IG 3 |
| ---------------- | ------------------------------------------------------------------- | ---- | ---- | ---- |
| v8               | 8.5 Collect Detailed Audit Logs                                     |      | X    | X    |
| v7               | 14.9 Enforce Detail Logging for Access or Changes to Sensitive Data |      |      | X    |

MITRE ATT&CK Mappings: T1562, T1562.006 / TA0007 / M1047