Grav is Vulnerable to XXE via SVG Upload

Dear Grav Security Team,

A security vulnerability was discovered in Grav CMS that allows authenticated attackers to read arbitrary files from the server through XML External Entity (XXE) injection.

Vulnerability Summary

| Field | Details | |-------|---------| | Vulnerability Type | XML External Entity (XXE) Injection | | Severity | High (CVSS 7.5) | | Affected Versions | Grav CMS <= 1.7.x | | Affected Component | SVG file upload/processing | | CWE | CWE-611: Improper Restriction of XML External Entity Reference | | Authentication Required | Yes (Admin panel access) |

Technical Details

Root Cause The application uses simplexml_load_string() to process uploaded SVG files without disabling external entity loading. This allows attackers to inject XXE payloads that are processed by the XML parser.

Vulnerable Code Pattern

// Current (Vulnerable):
$svg = simplexml_load_string($content);

// No LIBXML_NOENT flag or entity loader protection

Attack Vector

1. Attacker authenticates to Grav admin panel
2. Uploads malicious SVG file via Pages → Media or File Manager plugin
3. Server parses SVG and processes XXE entities
4. Arbitrary file contents are exfiltrated

Impact

An authenticated attacker can:

1. Read sensitive files:

   • /etc/passwd - System user information
   • user/accounts/*.yaml - Admin credentials and 2FA secrets
   • user/config/system.yaml - System configuration
   • .env files - Environment secrets and API keys

2. Perform SSRF - Access internal services via external entity URLs

3. Potential DoS - Billion laughs attack via recursive entity expansion

Proof of Concept

Malicious SVG Payload

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg [
  <!ENTITY xxe SYSTEM "file:///etc/passwd">
]>
<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
  <text x="10" y="50">&xxe;</text>
</svg>

Steps to Reproduce

1. Login to Grav CMS admin panel
2. Navigate to Pages → select any page → Media tab
3. Upload the malicious SVG file
4. Observe file contents in response/error or stored output

Recommended Fix

Option 1: Add XXE Protection Flags

libxml_use_internal_errors(true);
$svg = simplexml_load_string($content, 'SimpleXMLElement', LIBXML_NOENT | LIBXML_DTDLOAD);

Option 2: Use SVG Sanitizer Library (Recommended)

use enshrined\svgSanitize\Sanitizer;

$sanitizer = new Sanitizer();
$sanitizer->removeRemoteReferences(true);
$cleanSVG = $sanitizer->sanitize($content);

The enshrined/svg-sanitize library properly strips XXE payloads and other malicious SVG content.

Request

1. Please acknowledge receipt of this report within 5 business days
2. Please provide an estimated timeline for a security patch
3. I am happy to assist with testing the fix
4. I request a CVE be assigned for this vulnerability
5. If you have a security advisory process, please include me in the credits

Turki Almatrafi.

---

Maintainer note — fix applied (2026-04-24)

Fixed across two repos:

1. Grav core on the 2.0 branch (commit 5a12f9be8, ships in 2.0.0-beta.2) — VectorImageMedium::__construct (the code path that reads width/height from an uploaded SVG) now strips <!DOCTYPE> and <!ENTITY> declarations before parsing, and calls simplexml_load_string with LIBXML_NONET | LIBXML_NOERROR | LIBXML_NOWARNING. On PHP < 8 it also calls libxml_disable_entity_loader(true) for the duration of the parse.

2. rhukster/dom-sanitizer (commit 02d08ec) — the library Grav ships as its SVG sanitizer. loadDocument now applies the same DOCTYPE/ENTITY strip and passes LIBXML_NONET to loadXML/loadHTML.

With both layers in place, the PoC:

<!DOCTYPE svg [
  <!ENTITY xxe SYSTEM "file:///etc/passwd">
]>
<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
  <text x="10" y="50">&xxe;</text>
</svg>

no longer expands &xxe;, and the parser cannot make outbound filesystem or network requests for external entities/DTDs. Billion-laughs-style entity expansion is also neutralized because the declarations are stripped before libxml ever sees them.

Files:

• system/src/Grav/Common/Page/Medium/VectorImageMedium.php.
• tests/unit/Grav/Common/Security/SvgXxeSecurityTest.php — XXE neutralization + billion-laughs + plain-SVG regression.
• dom-sanitizer: src/DOMSanitizer.php + two new XXE tests in its own suite.