Package manager spawning a shell or interpreter on Linux

Siemphony@siemphonylowT1204.005unverified

Matches AN0698's Linux leg: a pip, npm, poetry or gem install spawning a shell or interpreter, the step MITRE describes as an install-time or startup-linked payload running. The prior selector matched ParentImage directly against '/pip', '/npm', '/gem' and similar — but none of those tools are their own process image on Linux. pip/pip3 and poetry are Python console-script entry points whose file opens with a shebang line, npm/npx are JS files shebanged '#!/usr/bin/env node', and gem is a Ruby script shebanged to ruby: the kernel loads the interpreter named on the shebang line as the process's actual image, so ParentImage is always python3 (or python), node, or ruby — never the tool name itself, regardless of how well the parent link is resolved. This rule instead matches the interpreter as ParentImage together with the package-manager entry point appearing in ParentCommandLine, the shape a shebang re-exec actually produces, e.g. `/usr/bin/python3 /usr/bin/pip3 install <pkg>` or `node /usr/lib/node_modules/npm/bin/npm-cli.js install <pkg>`. conda is dropped from this selector entirely: most installs wire `conda` as a bash *function* sourced into the shell's rc file rather than a standalone binary, so a child it "spawns" shows ParentImage=bash with nothing in ParentCommandLine reliably distinguishing a conda install from any other shell activity — catching that form needs a shell-history or session-scoped correlation this rule does not attempt, and is out of scope here rather than silently assumed to be covered. PREREQUISITE — raw auditd is not enough. A SYSCALL execve record carries the process's own `exe=`, a numeric `ppid`, and its own argv, but no parent executable path or parent command line at all, so both ParentImage and ParentCommandLine are unpopulated and this rule returns zero rows unless the process_creation pipeline is fed by something that resolves and joins the parent record for you: Auditbeat's `process.parent.executable` enrichment plus a ppid-to-execve join for the parent's own argv, sysmon-for-linux (whose EventID 1 emits both ParentImage and ParentCommandLine directly), or an EDR normalisation layer doing the same work. On unenriched auditd, zero rows here means blind, not quiet. AN0698's other leg — new script files under ~/.local or ~/.cache within 5 minutes of install — is a correlation across a separate auditd PATH record with no filename field offered here, so only the process-spawn leg is written; the Windows leg (AN0699) is the same parent/child shape already published as T1195.001 and is not repeated. A postinstall hook that writes its payload and defers execution to cron, a systemd unit or a detached shell breaks the parent-child pair and is invisible here even with the enrichment in place. UNVERIFIED AS AUTHORED — derived from MITRE ATT&CK DET0252, not hand-written and not tested by its author. Any lab result is on this rule's own page.Full description

The 4 SIEM queries below are previews produced by Siemphony’s own translator, not pySigma, and none has been executed against a real backend — review before you deploy.

detection.yml

Sentinel · KQL

Run this as a search.

DeviceProcessEvents| where (((((InitiatingProcessFolderPath endswith "/python3" or InitiatingProcessFolderPath endswith "/python") and (InitiatingProcessCommandLine contains "pip" or InitiatingProcessCommandLine contains "poetry")) or (InitiatingProcessFolderPath endswith "/node" and (InitiatingProcessCommandLine contains "npm" or InitiatingProcessCommandLine contains "npx"))) or (InitiatingProcessFolderPath endswith "/ruby" and InitiatingProcessCommandLine contains "gem")) and (FolderPath endswith "/sh" or FolderPath endswith "/bash" or FolderPath endswith "/dash" or FolderPath endswith "/python3" or FolderPath endswith "/python" or FolderPath endswith "/node" or FolderPath endswith "/curl" or FolderPath endswith "/wget" or FolderPath endswith "/perl"))

Splunk · SPL

Run this as a search.

index=* (((((ParentImage="*/python3" OR ParentImage="*/python") AND (ParentCommandLine="*pip*" OR ParentCommandLine="*poetry*")) OR (ParentImage="*/node" AND (ParentCommandLine="*npm*" OR ParentCommandLine="*npx*"))) OR (ParentImage="*/ruby" AND ParentCommandLine="*gem*")) AND (Image="*/sh" OR Image="*/bash" OR Image="*/dash" OR Image="*/python3" OR Image="*/python" OR Image="*/node" OR Image="*/curl" OR Image="*/wget" OR Image="*/perl"))

Elastic · ES|QL

Run this as a search.

FROM logs-*| WHERE (((((TO_LOWER(process.parent.executable) LIKE "*/python3" OR TO_LOWER(process.parent.executable) LIKE "*/python") AND (TO_LOWER(process.parent.command_line) LIKE "*pip*" OR TO_LOWER(process.parent.command_line) LIKE "*poetry*")) OR (TO_LOWER(process.parent.executable) LIKE "*/node" AND (TO_LOWER(process.parent.command_line) LIKE "*npm*" OR TO_LOWER(process.parent.command_line) LIKE "*npx*"))) OR (TO_LOWER(process.parent.executable) LIKE "*/ruby" AND TO_LOWER(process.parent.command_line) LIKE "*gem*")) AND (TO_LOWER(process.executable) LIKE "*/sh" OR TO_LOWER(process.executable) LIKE "*/bash" OR TO_LOWER(process.executable) LIKE "*/dash" OR TO_LOWER(process.executable) LIKE "*/python3" OR TO_LOWER(process.executable) LIKE "*/python" OR TO_LOWER(process.executable) LIKE "*/node" OR TO_LOWER(process.executable) LIKE "*/curl" OR TO_LOWER(process.executable) LIKE "*/wget" OR TO_LOWER(process.executable) LIKE "*/perl"))

Wazuh · XML rule

Deploy to your manager — this is a rule, not a search.

<group name="sigma,linux,process_creation,">  <!-- Rule ids must be unique on your manager; 100000+ is the user range. -->  <!-- 3 rules: the Sigma condition ORs across different fields,       which one rule cannot express. Any one matching is a hit. -->  <rule id="100000" level="5">    <!-- Set <if_sid> to the decoder/base rule for linux so this only evaluates relevant events. -->    <field name="ParentImage" type="pcre2">(?i)(/python3$|/python$)</field>    <field name="ParentCommandLine" type="pcre2">(?i)(pip|poetry)</field>    <field name="Image" type="pcre2">(?i)(/sh$|/bash$|/dash$|/python3$|/python$|/node$|/curl$|/wget$|/perl$)</field>    <description>Package manager spawning a shell or interpreter on Linux (1/3)</description>    <mitre>      <id>T1204.005</id>    </mitre>  </rule>   <rule id="100001" level="5">    <!-- Set <if_sid> to the decoder/base rule for linux so this only evaluates relevant events. -->    <field name="ParentImage" type="pcre2">(?i)/node$</field>    <field name="ParentCommandLine" type="pcre2">(?i)(npm|npx)</field>    <field name="Image" type="pcre2">(?i)(/sh$|/bash$|/dash$|/python3$|/python$|/node$|/curl$|/wget$|/perl$)</field>    <description>Package manager spawning a shell or interpreter on Linux (2/3)</description>    <mitre>      <id>T1204.005</id>    </mitre>  </rule>   <rule id="100002" level="5">    <!-- Set <if_sid> to the decoder/base rule for linux so this only evaluates relevant events. -->    <field name="ParentImage" type="pcre2">(?i)/ruby$</field>    <field name="ParentCommandLine" type="pcre2">(?i)gem</field>    <field name="Image" type="pcre2">(?i)(/sh$|/bash$|/dash$|/python3$|/python$|/node$|/curl$|/wget$|/perl$)</field>    <description>Package manager spawning a shell or interpreter on Linux (3/3)</description>    <mitre>      <id>T1204.005</id>    </mitre>  </rule></group>

At a glance

Logsource: process_creation / linux
Level: low
Category: office_macro_execution
Sigma status: experimental
Backends: 4 of 4 rendered
Updated: 30 Aug 2026
Rule ID: ed52b230-1c45-48ad-a289-dc616f4eb252

ATT&CKT1204.005

T1204.005Malicious Library

ATT&CK® is a registered trademark of The MITRE Corporation. These mappings are the rule author’s, and are neither reviewed nor endorsed by MITRE.

Lessonoffice macro execution

office macro execution

01 · What this rule detects

A document application — Word, Excel, PowerPoint, Outlook, Publisher, Visio — starting a shell, a script host or a signed proxy binary. The document is the delivery vehicle and the child process is the first thing the attacker actually controls. It is one of the most durable detections available because the parent-child relationship is a property of how the payload has to run, not a string the attacker chooses.

02 · Telemetry you need

Process creation with ParentImage and the full command line — Sysmon EventID 1, or Security 4688 with Audit Process Creation plus the command-line inclusion policy; both off by default, and 4688 without the second one gives you the child process with no arguments
Sysmon EventID 7 (ImageLoad) for the macro runtime — VBE7.DLL and its companions loading into an Office process tells you a macro ran even when nothing was spawned
Sysmon EventID 11 (FileCreate) under %TEMP%, INetCache and the Outlook secure temp folder, where the attachment lands before it is opened
Sysmon EventID 15 (FileCreateStreamHash) for the Mark of the Web zone identifier, which records that the document arrived from outside
Sysmon EventID 3 (NetworkConnect) initiated by the Office process itself

03 · How the logic works

The rule is ParentImage in the Office set AND Image in a child set — shells, script hosts, the signed proxy binaries, and any process launched from a user-writable path. ParentImage carries the signal; the child list is the part you widen over time. The important weakness to teach is that the parent link is breakable: a macro that goes through WMI or a COM object gets its child reparented away from Office, and the rule silently stops matching for exactly the samples that bothered to evade it. That is why the macro-runtime image load and Office writing an executable file are worth having as separate rules rather than as extra conditions on this one — they survive the reparenting. Outlook deserves its own rule too: as a parent it means something different from Word, and the volume profile is different.

04 · Common false positives

Genuine business macros — finance and reporting workbooks that shell out, refresh external data or drive another application
Office add-ins and vendor integrations that launch helper processes, including document management and e-signature tooling
Mail merge, document conversion and reporting pipelines that automate Office on a server
Helpdesk and repair scripts that invoke Office repair or start a shell from a template
Office spawning ordinary Windows infrastructure processes as part of normal operation

05 · Detection maturity

Tier 1 — starting point: Matches an Office application spawning cmd.exe or PowerShell.
Tier 2 — tuned: Covers the full parent set against a broad child set including script hosts and proxy binaries, with named business macros excluded by document path.
Tier 3 — correlated: Adds the macro runtime load and the Mark of the Web, and correlates the chain with what the child process did on the network or wrote to disk.

Tuning & false positivesexperimental · 3 declared

experimental (current stage)
test
stable

Written and reasoned about, but not yet run against real telemetry. Expect to tune it before trusting it.

Tuning tips

Exclude by the document or template path, or by the host running the automation, rather than by the child process — dropping cmd.exe from the child list to quieten one workbook blinds the rule everywhere
Raise severity when the document carries a Mark of the Web zone identifier, and again when it came from Outlook's temp folder
Keep the child list additive, and include 'anything launched from a user-writable directory' as a condition rather than trying to name every binary
Give outlook.exe as parent its own rule so the two can be tuned and prioritised independently
Where the telemetry has it, capture the grandparent as well, so the alert shows the analyst the whole chain rather than one hop

Declared by the author

Native-extension builds. Python wheels needing a source build and npm packages using node-gyp legitimately spawn sh, python3, bash, curl or wget during an ordinary pip or npm install — the curl/wget calls fetch vendored source tarballs or build dependencies — on a developer or CI host this is the loudest source and needs a toolchain allowlist to separate from a malicious postinstall hook.
PEP 517/518 build-backend invocation. pip and poetry resolving a package's build system spawn a python or python3 subprocess for every source distribution installed, which is standard behaviour and will match selection_manager_pip and selection_payload together on every such install.
gem installing a native extension, which runs extconf.rb through a spawned sh or make step during ordinary Ruby gem installation.

Noise check0 of 4 fired

Fires on none of the 4 ordinary behaviours the baseline holds for this log type. That is not a precision guarantee: it means only not caught by these 4 behaviours, and the next ordinary behaviour nobody wrote down may still match.

Run live against 65 hand-written events of ordinary corporate activity — backup agents, software distribution, patching, helpdesk scripts, EDR. It says nothing about how often the rule would fire in production, which is the number that actually exhausts an analyst.

Verification1 run

Not verified

Siemphony benign baseline
completed
Siemphony IR · 3 Sept 2026
No events matched, so this run proves nothing either way.

Test it yourselfin your browser

Runs here in your browser against public attack recordings. A preview — not the verification badge.

Recordings of T1204.005, evaluated against their process_creation events.

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Package manager spawning a shell or interpreter on Linux

The detection

detection.yml

Sentinel · KQL

Splunk · SPL

Elastic · ES|QL

Wazuh · XML rule

Community

Verdicts from engineers who deployed it