Linux Magic SysRq Key Abuse

Status: production
Severity: medium
Group by: audit_id, current_working_directory, dest, host, match_count, reconstructed_path
Author: Milad Cheraghi
Source: github.com/splunk/security_content

Detects potential abuse of the Linux Magic SysRq (System Request) key by adversaries with root or sufficient privileges to manipulate or destabilize a system. Writing to /proc/sysrq-trigger can crash the system, kill processes, or bypass standard logging. Monitoring SysRq abuse helps detect stealthy post-exploitation activity. Correlate with related EXECVE or PROCTITLE events to identify the process or user responsible for the access or modification.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.004` Command and Scripting Interpreter: Unix Shell
Impact	`T1489` Service Stop, `T1499` Endpoint Denial of Service, `T1529` System Shutdown/Reboot

Rule body splunk

name: Linux Magic SysRq Key Abuse
id: 22c03600-f84a-47fa-abaa-ffbe3e72c782
version: 5
creation_date: '2025-08-28'
modification_date: '2026-05-13'
author: Milad Cheraghi
status: production
type: TTP
description: |
    Detects potential abuse of the Linux Magic SysRq (System Request) key by adversaries with root or sufficient privileges to manipulate or destabilize a system.
    Writing to /proc/sysrq-trigger can crash the system, kill processes, or bypass standard logging.
    Monitoring SysRq abuse helps detect stealthy post-exploitation activity.
    Correlate with related EXECVE or PROCTITLE events to identify the process or user responsible for the access or modification.
data_source:
    - Linux Auditd Path
    - Linux Auditd Cwd
search: |
    `linux_auditd`
    (type=PATH OR type=CWD)
    | rex "msg=audit\([^)]*:(?<audit_id>\d+)\)"
    
    | stats
      values(type) as types
      values(name) as names
      values(nametype) as nametype
      values(cwd) as cwd_list
      values(_time) as event_times
      by audit_id, host
    
    | eval current_working_directory = coalesce(mvindex(cwd_list, 0), "N/A")
    | eval candidate_paths = mvmap(names, if(match(names, "^/"), names, current_working_directory + "/" + names))
    | eval matched_paths = mvfilter(match(candidate_paths, ".*/proc/sysrq-trigger|.*/proc/sys/kernel/sysrq|.*/etc/sysctl.conf"))
    | eval match_count = mvcount(matched_paths)
    | eval reconstructed_path = mvindex(matched_paths, 0)
    | eval e_time = mvindex(event_times, 0)
    | where match_count > 0
    | rename host as dest
    
    | stats count min(e_time) as firstTime max(e_time) as lastTime
      values(nametype) as nametype
      by current_working_directory
         reconstructed_path
         match_count
         dest
         audit_id
    
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `linux_magic_sysrq_key_abuse_filter`
how_to_implement: |
    To implement this detection, ensure auditd is configured to watch:
      - /proc/sysrq-trigger
      - /proc/sys/kernel/sysrq
      - /etc/sysctl.conf
    with write and attribute changes (`-p wa`) and key `sysrq`. Make sure the type=CWD record type is activate in your auditd configuration and
    Use the Splunk Add-on for Unix and Linux for proper ingestion and CIM normalization.
    This enables effective monitoring of Linux endpoints for SysRq abuse.
known_false_positives: |
    Legitimate administrative activity modifying SysRq for debugging or recovery.
    Please update the filter macros to remove false positives.
references:
    - https://www.kernel.org/doc/html/v4.10/_sources/admin-guide/sysrq.txt
    - https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/4/html/reference_guide/s3-proc-sys-kernel
    - https://www.splunk.com/en_us/blog/security/threat-update-awfulshred-script-wiper.html
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search dest="$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
finding:
    title: Abuse of the Linux Magic System Request key detected on host - [$dest$]
    entity:
        field: dest
        type: system
        score: 50
analytic_story:
    - Compromised Linux Host
asset_type: Endpoint
mitre_attack_id:
    - T1059.004
    - T1529
    - T1489
    - T1499
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1529/auditd_path_sysrq/path_sysrq.log
          source: auditd
          sourcetype: auditd
      test_type: unit

Stages and Predicates

Stage 1: `search`

`linux_auditd`
(type=PATH OR type=CWD)

Stage 2: `rex`

| rex "msg=audit\([^)]*:(?<audit_id>\d+)\)"

Stage 3: `stats`

| stats
  values(type) as types
  values(name) as names
  values(nametype) as nametype
  values(cwd) as cwd_list
  values(_time) as event_times
  by audit_id, host

Stage 4: `eval`

| eval current_working_directory = coalesce(mvindex(cwd_list, 0), "N/A")

Stage 5: `eval`

| eval candidate_paths = mvmap(names, if(match(names, "^/"), names, current_working_directory + "/" + names))

Stage 6: `eval`

| eval matched_paths = mvfilter(match(candidate_paths, ".*/proc/sysrq-trigger|.*/proc/sys/kernel/sysrq|.*/etc/sysctl.conf"))

Stage 7: `eval`

| eval match_count = mvcount(matched_paths)

Stage 8: `eval`

| eval reconstructed_path = mvindex(matched_paths, 0)

Stage 9: `eval`

| eval e_time = mvindex(event_times, 0)

Stage 10: `where`

| where match_count > 0

Stage 11: `rename`

| rename host as dest

Stage 12: `stats`

| stats count min(e_time) as firstTime max(e_time) as lastTime
  values(nametype) as nametype
  by current_working_directory
     reconstructed_path
     match_count
     dest
     audit_id

Stage 13: `search`

| `security_content_ctime(firstTime)`

Stage 14: `search`

| `security_content_ctime(lastTime)`

Stage 15: `search`

| `linux_magic_sysrq_key_abuse_filter`

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`match_count`	gt	`0`
`sourcetype`	eq	`auditd`
`type`	eq	`CWD` `PATH`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Linux Magic SysRq Key Abuse

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: `search`

Stage 2: `rex`

Stage 3: `stats`

Stage 4: `eval`

Stage 5: `eval`

Stage 6: `eval`

Stage 7: `eval`

Stage 8: `eval`

Stage 9: `eval`

Stage 10: `where`

Stage 11: `rename`

Stage 12: `stats`

Stage 13: `search`

Stage 14: `search`

Stage 15: `search`

Indicators

Keyboard shortcuts

Search operators

Linux Magic SysRq Key Abuse

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: search

Stage 2: rex

Stage 3: stats

Stage 4: eval

Stage 5: eval

Stage 6: eval

Stage 7: eval

Stage 8: eval

Stage 9: eval

Stage 10: where

Stage 11: rename

Stage 12: stats

Stage 13: search

Stage 14: search

Stage 15: search

Indicators

Stage 1: `search`

Stage 2: `rex`

Stage 3: `stats`

Stage 4: `eval`

Stage 5: `eval`

Stage 6: `eval`

Stage 7: `eval`

Stage 8: `eval`

Stage 9: `eval`

Stage 10: `where`

Stage 11: `rename`

Stage 12: `stats`

Stage 13: `search`

Stage 14: `search`

Stage 15: `search`