CVE-2026-62672: Grav Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-37f3-6p89-6qr9",
  "modified" : "2026-09-17T16:34:43Z",
  "published" : "2026-09-02T14:50:57Z",
  "aliases" : [ "CVE-2026-62672" ],
  "summary" : "Grav: Authenticated ReDoS via regex_replace in Twig Sandbox",
  "details" : "### Summary\n\nThe `regex_replace` filter and function are allowlisted in Grav's Twig content sandbox. When Twig processing in page content is enabled `security.twig_content.process_enabled: true`, authenticated page editors can supply a catastrophically backtracking PCRE pattern, causing unbounded CPU consumption and denying service to the entire web server process.\n\n---\n\n### Details\n\nThe Twig sandbox allowlists, defined in `system/config/security.yaml`, explicitly include `regex_replace` in both the filter and function permission lists:\n\n**Source: `system/config/security.yaml`**\n\n```yaml\ntwig_sandbox:\n  allowed_filters:\n    # ...\n    - regex_replace    #  user-controlled pattern allowed in sandbox\n  allowed_functions:\n    # ...\n    - regex_replace    #  same\n```\n\nThe underlying implementation passes the caller-controlled `$pattern` directly into PHP's `preg_replace()` without any pattern complexity validation:\n\n**Source: `system/src/Grav/Common/Twig/Extension/GravExtension.php:1317-1319`**\n\n```php\npublic function regexReplace($subject, $pattern, $replace, $limit = -1)\n{\n    return preg_replace($pattern, $replace, $subject, $limit);\n}\n```\n\nWhen `twig_content.process_enabled` is `true`, page body content is sandboxed but can use any allowlisted filter. An editor who embeds a catastrophic backtracking pattern causes the PCRE engine to enter exponential time complexity, consuming 100% CPU until the PHP process is killed or the request times out.\n\n**Conditions required**:\n1. `security.twig_content.process_enabled: true` (opt-in, `false` by default on fresh 2.0 installs)\n2. `security.twig_sandbox.enabled: true` (default) - the function is reachable under sandbox\n3. Attacker must have page edit access (authenticated contributor / editor role)\n\n---\n\n### PoC\n\n**Configuration prerequisite** - enable Twig in content:\n\n```yaml\n# user/config/security.yaml\ntwig_content:\n  process_enabled: true\n```\n\n**Payload** — embed in any Grav page body with `process: { twig: true }` in frontmatter:\n\n```\n---\ntitle: Test\nprocess:\n  twig: true\n---\n{{ 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab'|regex_replace('/^(a+)+$/', '') }}\n```\n\nOr as a function call in a page where the editor has Twig access:\n\n```twig\n{{ regex_replace('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab', '/^(a+)+$/', '') }}\n```\n\n**Result**: The PHP-FPM worker (or CLI server process) enters catastrophic PCRE backtracking. On a 2 GHz host, a 32-character string with the above pattern will exhaust one CPU core for seconds to minutes. With a slightly longer string, the time grows exponentially.\n\n---\n\n### Impact\n\n**Vulnerability type**: Regular Expression Denial of Service - ReDoS\n\n**Who is impacted**: Server availability. Any Grav installation where:\n- An editor-role account exists (or has been compromised), AND\n- The operator has enabled `twig_content.process_enabled: true`\n\nAn attacker with page-edit access can render the site unresponsive for all visitors by publishing a page with a catastrophic regex. On single-worker PHP configurations this is a complete outage. On multi-worker setups, multiple concurrent page renders of the malicious page can saturate all workers.\n\n---",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "getgrav/grav"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.0.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/security/advisories/GHSA-37f3-6p89-6qr9"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-62672"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/commit/907116268ad4f48be7472c57f64981918578599a"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/getgrav/grav"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/releases/tag/2.0.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-02T14:50:57Z",
    "nvd_published_at" : "2026-08-19T16:18:20Z"
  }
}