Linux capsh Shell Execution via Shell-Spawn Command Line Ending With " --"

Alerts on Linux executions of /capsh with a command line ending in " --", consistent with shell invocation attempts.

FreeReviewedSigma · High · v3

Product: linux
Category: process_creation
Author: Li Ling, Andy Parkidomo, Robert Rakowski, Blake Hartstein (Bloomberg L.P.) (SigmaHQ), DRL 1.1
Published: 2024-09-02
Updated: 2026-07-31

ATT&CK techniques

Execution

Recon
Resource Dev
Initial Access
Execution
- T1059Command and Scripting Interpreter
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags Linux process executions where the binary path ends with "/capsh" and the command line ends with " --", indicating an attempt to use capsh to spawn a shell. Attackers may leverage capsh to break out of restricted environments or gain interactive command execution. The detection relies on process creation telemetry, specifically the process image path and the full command line.

Reporting behind it

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Linux capsh Shell Execution via Shell-Spawn Command Line Ending With " --"

Pivot detection · T1059 · 9 related

Changelog

v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

linux-capsh-invoked-with-shell-commandline-pattern-db1ac3be

title: Linux capsh Shell Execution via Shell-Spawn Command Line Ending With " --"
id: 14037ebb-7aaf-453d-a070-6146d6b5a17a
status: test
description: This rule flags Linux process executions where the binary path ends with "/capsh" and the command line ends with " --", indicating an attempt to use capsh to spawn a shell. Attackers may leverage capsh to break out of restricted environments or gain interactive command execution. The detection relies on process creation telemetry, specifically the process image path and the full command line.
references:
  - https://gtfobins.github.io/gtfobins/capsh/#shell
  - https://www.elastic.co/guide/en/security/current/linux-restricted-shell-breakout-via-linux-binary-s.html
  - https://github.com/SigmaHQ/sigma/blob/master/rules/linux/process_creation/proc_creation_lnx_capsh_shell_invocation.yml
author: Li Ling, Andy Parkidomo, Robert Rakowski, Blake Hartstein (Bloomberg L.P.), Huntrule Team
date: 2024-09-02
tags:
  - attack.execution
  - attack.t1059
logsource:
  category: process_creation
  product: linux
detection:
  selection:
    Image|endswith: /capsh
    CommandLine|endswith: " --"
  condition: selection
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: db1ac3be-f606-4e3a-89e0-9607cbe6b98a
    type: derived

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