CVE-2026-56701

描述

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 ```php // 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 <?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 ```php libxml_use_internal_errors(true); $svg = simplexml_load_string($content, 'SimpleXMLElement', LIBXML_NOENT | LIBXML_DTDLOAD); ``` Option 2: Use SVG Sanitizer Library (Recommended) ```php 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`](https://github.com/getgrav/grav/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`](https://github.com/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: ```xml <!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`](https://github.com/getgrav/grav/blob/2.0/system/src/Grav/Common/Page/Medium/VectorImageMedium.php). - [`tests/unit/Grav/Common/Security/SvgXxeSecurityTest.php`](https://github.com/getgrav/grav/blob/2.0/tests/unit/Grav/Common/Security/SvgXxeSecurityTest.php) — XXE neutralization + billion-laughs + plain-SVG regression. - dom-sanitizer: [`src/DOMSanitizer.php`](https://github.com/rhukster/dom-sanitizer/blob/main/src/DOMSanitizer.php) + two new XXE tests in its own suite.