Clear or Disable Kernel Ring Buffer Logs via Syslog Syscall

Description

Detects the use of the syslog syscall with action code 5 (SYSLOG_ACTION_CLEAR), (4 is SYSLOG_ACTION_READ_CLEAR and 6 is SYSLOG_ACTION_CONSOLE_OFF) which clears the kernel ring buffer (dmesg logs). This can be used by attackers to hide traces after exploitation or privilege escalation. A common technique is running dmesg -c, which triggers this syscall internally.

Query · sigma

selection:
  type: SYSCALL
  SYSCALL: syslog
  a0:
  - 4
  - 5
  - 6
condition: selection

Known false positives

  • System administrators or scripts that intentionally clear logs
  • Debugging scripts
Raw source Clear or Disable Kernel Ring Buffer Logs via Syslog Syscall · Sigma
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Published by SigmaHQ/sigma ↗, licensed under Detection Rule License 1.1 ↗. Reproduced here unmodified. 
title: Clear or Disable Kernel Ring Buffer Logs via Syslog Syscall
id: eca5e022-d368-4043-98e5-9736fb01f72f
status: experimental
description: |
    Detects the use of the `syslog` syscall with action code 5 (SYSLOG_ACTION_CLEAR),
    (4 is SYSLOG_ACTION_READ_CLEAR and 6 is SYSLOG_ACTION_CONSOLE_OFF) which clears the kernel
    ring buffer (dmesg logs). This can be used by attackers to hide traces after exploitation
    or privilege escalation. A common technique is running `dmesg -c`, which triggers this syscall internally.
references:
    - https://man7.org/linux/man-pages/man2/syslog.2.html
    - https://man7.org/linux/man-pages/man1/dmesg.1.html
author: Milad Cheraghi
date: 2025-05-27
modified: 2025-12-05
tags:
    - attack.defense-impairment
    - attack.t1685.006
logsource:
    product: linux
    service: auditd
    definition: |
        Required auditd configuration:
        -a always,exit -F arch=b64 -S syslog -F a0=4 -k clear_dmesg_logs
        -a always,exit -F arch=b64 -S syslog -F a0=5 -k clear_dmesg_logs
        -a always,exit -F arch=b64 -S syslog -F a0=6 -k disable_dmesg_logs
        -a always,exit -F arch=b32 -S syslog -F a0=4 -k clear_dmesg_logs
        -a always,exit -F arch=b32 -S syslog -F a0=5 -k clear_dmesg_logs
        -a always,exit -F arch=b32 -S syslog -F a0=6 -k disable_dmesg_logs
detection:
    selection:
        type: 'SYSCALL'
        SYSCALL: 'syslog'
        a0:
            - 4 # SYSLOG_ACTION_READ_CLEAR : Read and clear log
            - 5 # SYSLOG_ACTION_CLEAR: Clear kernel ring buffer (without reading)
            - 6 # SYSLOG_ACTION_CONSOLE_OFF: Disable logging to console
    condition: selection
falsepositives:
    - System administrators or scripts that intentionally clear logs
    - Debugging scripts
level: medium

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