{"id":"GHSA-9695-8fr9-hw5q","summary":"Grav Vulnerable to Publisher-Level Stored XSS via Unquoted Event Attributes","details":"### Summary\nA stored Cross-Site Scripting (XSS) vulnerability in `getgrav/grav` allows publisher-level accounts to execute arbitrary JavaScript. The issue arises from a blacklist bypass in the `detectXss()` function when handling unquoted HTML event attributes.\n\n### Details\nThe `detectXss()` function relies on a blacklist pattern to filter malicious attributes. The specific regex pattern used to match `on*` events is flawed:\n```php\n'on_events' =\u003e '#(\u003c[^\u003e]+[a-z\\x00-\\x20\\\"\\'\\/])(on[a-z]+|xmlns)\\s*=[\\s|\\'\\\"].*[\\s|\\'\\\"]\u003e#iUu'\n```\nThis pattern fails to properly identify `on*` event handlers that are constructed without quotation marks. This allows an attacker to completely bypass the filter. *Note: It is highly recommended to replace this blacklist approach with a robust, established HTML sanitization library.*\n\n### PoC\nAn attacker with publisher-level access can reproduce this by injecting the following payload into any vulnerable content field:\n```html\n\u003cimg src=x onerror=eval(atob(/YWxlcnQoZG9jdW1lbnQuY29va2llKQ/.source))\u003e\n```\n\u003cimg width=\"1889\" height=\"482\" alt=\"image1\" src=\"https://github.com/user-attachments/assets/0f1a339b-25a8-4b6e-91af-8c59e6a39297\" /\u003e\n\u003cimg width=\"3055\" height=\"920\" alt=\"image2\" src=\"https://github.com/user-attachments/assets/12680058-bbb3-4446-b58e-515533bb4e90\" /\u003e\n\u003cimg width=\"2909\" height=\"1339\" alt=\"image3\" src=\"https://github.com/user-attachments/assets/c7ed7e61-8dcf-402d-8589-98d18978c71a\" /\u003e\n\n\n**Execution Details:**\nThe `onerror` event is written without quotes to bypass the regex. Because unquoted attributes are restricted in their character usage (e.g., the `=` symbol cannot be used easily), the payload leverages `atob()` and regex `.source` to decode the base64 string `YWxlcnQoZG9jdW1lbnQuY29va2llKQ` (which translates to `alert(document.cookie)`). The `atob()` function conveniently auto-completes the necessary `=` padding for the base64 string.\n\n### Impact\n- **Vulnerability Type:** Stored Cross-Site Scripting (XSS)\n- **Impacted Parties:** Any user (including administrators) who views the compromised content published by the attacker.\n- **Consequences:** Attackers can execute malicious scripts in a victim's browser, leading to session hijacking (cookie theft), unauthorized actions.\n\n\n---\n\n## Maintainer note — fix applied (2026-04-24)\n\nFixed in Grav core on the `2.0` branch: commit [`5a12f9be8`](https://github.com/getgrav/grav/commit/5a12f9be8) — will ship in **2.0.0-beta.2**.\n\n**What changed:** the `on_events` regex in `Security::detectXss()` no longer requires quotes or whitespace around `=`. The previous form:\n\n```\n'on_events' =\u003e '#(\u003c[^\u003e]+[\\s\\x00-\\x20\\\"\\'\\/])(on\\s*[a-z]+|xmlns)\\s*=[\\s|\\'\\\"].*[\\s|\\'\\\"]\u003e#iUu'\n```\n\nrequired `[\\s|'\"]` immediately after the `=`, so `\u003cimg src=x onerror=alert(1)\u003e` slid past. The new regex drops the value-matching tail entirely and just flags the presence of an `on*=` attribute anywhere inside a tag:\n\n```\n'on_events' =\u003e '#\u003c[^\u003e]*?[\\s\\x00-\\x20\\\"\\'\\/](on\\s*[a-z]+|xmlns)\\s*=#iu'\n```\n\nDetecting the attribute name + `=` is enough for a tripwire — the trade-off is occasional false positives on legitimate attribute *values* containing `on*=` substrings, which the maintainer can hand-approve.\n\nThis same regex bypass was the detection-layer half of GHSA-c2q3-p4jr-c55f and GHSA-w8cg-7jcj-4vv2; the fix here knocks both down.\n\n**Files:**\n- [`system/src/Grav/Common/Security.php`](https://github.com/getgrav/grav/blob/2.0/system/src/Grav/Common/Security.php).\n- [`tests/unit/Grav/Common/Security/DetectXssTest.php`](https://github.com/getgrav/grav/blob/2.0/tests/unit/Grav/Common/Security/DetectXssTest.php) — 18 cases: unquoted PoCs, quoted-form regression, safe-content negatives.","aliases":["CVE-2026-42612"],"modified":"2026-09-10T03:51:05.155510423Z","published":"2026-05-05T21:27:15Z","database_specific":{"github_reviewed_at":"2026-05-05T21:27:15Z","nvd_published_at":"2026-05-11T16:17:34Z","cwe_ids":["CWE-79"],"severity":"HIGH","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/getgrav/grav/security/advisories/GHSA-9695-8fr9-hw5q"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42612"},{"type":"WEB","url":"https://github.com/getgrav/grav/commit/5a12f9be8314682c8713e569e330f11805d0a663"},{"type":"PACKAGE","url":"https://github.com/getgrav/grav"}],"affected":[{"package":{"name":"getgrav/grav","ecosystem":"Packagist","purl":"pkg:composer/getgrav/grav"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.0-beta.2"}]}],"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-beta.1"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-9695-8fr9-hw5q/GHSA-9695-8fr9-hw5q.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N"}]}