Grav: .htaccess file extension rules bypass via case variation on case-insensitive filesystems

Summary

The default .htaccess shipped with Grav (and the reference webserver-configs/htaccess.txt) contains security rules that block direct HTTP access to sensitive file types (.yaml, .yml, .php, .json, .twig, etc.) under user/ and system/vendor/ directories. However, these rules lack the [NC] (No Case) flag, making them case-sensitive. On case-insensitive filesystems (Windows/NTFS, macOS/HFS+, or Linux with Docker volumes mounted from Windows/macOS), an attacker can bypass these rules by requesting files with uppercase extensions (e.g., .YAML, .PHP, .JSON).

Affected Versions

• Grav 2.0.1 (latest stable as of June 2026) — confirmed
• Grav 1.7.x — likely affected (same .htaccess rules)
• All versions shipping the current webserver-configs/htaccess.txt

Affected Component

File: .htaccess (root of Grav installation) Reference: webserver-configs/htaccess.txt

Affected Rules (lines 68, 70, 72)

# Line 68 — system/vendor file types
RewriteRule ^(system|vendor)/(.*)\.(txt|xml|md|html|htm|shtml|shtm|json|yaml|yml|php|php2|php3|php4|php5|phar|phtml|pl|py|cgi|twig|sh|bat)$ error [F]

# Line 70 — user file types
RewriteRule ^(user)/(.*)\.(txt|md|json|yaml|yml|php|php2|php3|php4|php5|phar|phtml|pl|py|cgi|twig|sh|bat)$ error [F]

# Line 72 — .md files globally
RewriteRule \.md$ error [F]

All three rules use [F] without [NC], making the extension match case-sensitive.

Steps to Reproduce

1. Install Grav on a system with a case-insensitive filesystem:

   • Windows (native WAMP/XAMPP)
   • macOS (default HFS+)
   • Docker on Windows/macOS with volume mounts (e.g., ./data:/var/www/html)

2. Create or use any plugin that stores sensitive data in its YAML config (e.g., API keys):

   user/plugins/my-plugin/my-plugin.yaml

3. Request the file with a case-varied extension:

   GET /user/plugins/my-plugin/my-plugin.YAML HTTP/1.1

4. Expected: HTTP 403 Forbidden

5. Actual: HTTP 200 OK — full file contents returned, including any API keys or sensitive configuration

Impact

• Information disclosure: Plugin configuration files (.yaml) containing API keys, credentials, or sensitive settings can be read by unauthenticated users
• Source code exposure: PHP source files can be downloaded (instead of executed) when requested with .PHP extension on some configurations
• Configuration exposure: user/config/system.yaml, user/config/site.yaml, and other system configuration files are accessible

Fix

Add the [NC] flag to the three affected rules:

RewriteRule ^(system|vendor)/(.*)\.(txt|xml|md|html|htm|shtml|shtm|json|yaml|yml|php|php2|php3|php4|php5|phar|phtml|pl|py|cgi|twig|sh|bat)$ error [F,NC]
RewriteRule ^(user)/(.*)\.(txt|md|json|yaml|yml|php|php2|php3|php4|php5|phar|phtml|pl|py|cgi|twig|sh|bat)$ error [F,NC]
RewriteRule \.md$ error [F,NC]

The [NC] flag makes the extension matching case-insensitive, covering .YAML, .Yaml, .PHP, .Json, etc.

Mitigating Factors

• On native Linux with ext4 filesystem (case-sensitive), the attack does not work because Apache cannot resolve the uppercase filename to the actual file
• Grav 2.0's Twig sandbox blocks access to plugins config subtree from page content, preventing SSTI-based config exfiltration
• The user/accounts/, user/config/, and user/data/ folders have separate rules (line 62, 66) that block ALL file types regardless of extension — these are not affected

Environment

• Grav: 2.0.1
• PHP: 8.3
• Apache: 2.4 with mod_rewrite
• OS: Docker (php:8.3-apache) with volume mounted from Windows 10 (NTFS)
• Tested: June 2026

Reporter

Sisnetic