{"id":"CVE-2026-62672","aliases":["CVE-2026-62237","GHSA-37f3-6p89-6qr9"],"url":"https://o3.security/vulnerability/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---","published":"2026-08-19T15:44:36.287Z","modified":"2026-10-16T02:48:02.005018127Z","cvss":null,"epss":{"score":0.00387,"percentile":0.32502,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"getgrav/grav","fixedVersion":"2.0.4"}],"fix":{"url":"https://github.com/getgrav/grav/commit/907116268ad4f48be7472c57f64981918578599a","label":"getgrav/grav@9071162"},"references":[{"type":"WEB","url":"https://github.com/getgrav/grav/releases/tag/2.0.4"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/62xxx/CVE-2026-62672.json"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/getgrav/grav/commit/907116268ad4f48be7472c57f64981918578599a"},{"type":"PACKAGE","url":"https://github.com/getgrav/grav"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-16T02:48:02.005018127Z"}}