GHSA-m8vh-v6r6-w7p6 Grav vulnerable to Denial of Service via Improper Input Handling in 'Supported' Parameter

• Packagist getgrav/grav: < 1.8.0-beta.27 → fixed in 1.8.0-beta.27

Endpoint: `admin/config/system` Submenu: `Languages` Parameter: `Supported` Application: Grav v 1.7.48 --- Summary A Denial of Service (DoS) vulnerability was identified in the "Languages" submenu of the Grav admin configuration panel (`/admin/config/system`). Specifically, the `Supported` parameter fails to properly validate user input. If a malformed value is inserted—such as a single forward slash (`/`) or an XSS test string—it causes a fatal regular expression parsing error on the server. This leads to application-wide failure due to the use of the `preg_match()` function with an improperly constructed regular expression, resulting in the following error: `preg_match(): Unknown modifier 'o' File: /system/src/Grav/Common/Language/Language.php line 244` Once triggered, the site becomes completely unavailable to all users. --- Details • Vulnerable Endpoint: `POST /admin/config/system` • Submenu: `Languages` • Parameter: `Supported` The application dynamically constructs a regular expression using the contents of the `Supported` field without escaping the input using `preg_quote()` or proper validation. This allows attackers to inject invalid syntax into the regex engine, crashing the application during language resolution. Stack trace excerpt: `Whoops \ Exception \ ErrorException (E_WARNING) preg_match(): Unknown modifier 'o' /system/src/Grav/Common/Language/Language.php244` --- Proof of Concept (PoC) Payloads: `/ ` Steps to Reproduce: 1. Log into the Grav Admin Panel. 2. Navigate to: Configuration → System → Languages. 3. Locate the `Supported` field. 4. Insert one of the payloads above (e.g., a single slash `/`). 5. Click Save. 1. Observe: All pages in the application begin throwing a fatal error and become inaccessible. --- Impact • Application-wide Denial of Service (DoS) • All login and admin views crash with the same error • Potentially exploitable by: • Admin panel users • CSRF if misconfigured --- References • CWE-1333: Improper Regular Expression • CWE-20: Improper Input Validation Discoverer Marcelo Queiroz by CVE-Hunters