hunt-file-upload

## 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 <?xml version="1.0"?> <svg xmlns="http://www.w3.org/2000/svg"> <script>alert(document.domain)</script> </svg> ``` --- ## ImageMagick / FFmpeg Exploitation ### ImageMagick SSRF / Fi...