Stored XSS via Hostile YouTube Video Title in AVideo YouTubeAPI Gallery Section

Summary

A stored Cross-Site Scripting vulnerability (CWE-79; chained CWE-829, Inclusion of Functionality from Untrusted Control Sphere) in the AVideo YouTubeAPI plugin renders the snippet.title field returned by the YouTube Data API into the homepage gallery markup with no HTML encoding. The title is set by the YouTube video uploader (anyone in the world) and is treated by AVideo as trusted content. A YouTube uploader who controls a video matching the operator's configured query injects HTML into the AVideo homepage by setting their video's title to a JavaScript-bearing string; the payload then executes in the browser of every visitor who loads any page that renders the gallery.

Details

plugin/YouTubeAPI/YouTubeAPI.php::listVideos() fetches search results from the YouTube Data API and stores the snippet.title field unchanged inside a YPTvideoObject:

// plugin/YouTubeAPI/YouTubeAPI.php (listVideos excerpt)
$searchResponse = $youtube->search->listSearch(
    'snippet,contentDetails,statistics', $options
);
foreach ($searchResponse['items'] as $searchResult) {
    $vid = new YPTvideoObject(
        $searchResult["id"]["videoId"],
        $searchResult['snippet']["title"],          // uploader-controlled
        $searchResult['snippet']["description"],
        $searchResult['snippet']["thumbnails"]["high"]["url"],
        $searchResult['snippet']["channelTitle"],
        "https://www.youtube.com/embed/{$searchResult['id']['videoId']}"
    );
    $object->videos[] = $vid;
}

plugin/YouTubeAPI/gallerySection.php then renders the title into three HTML contexts inside each gallery card. Four reflection sites total, three of them completely unprotected:

// plugin/YouTubeAPI/gallerySection.php (foreach body)
$youtubeTitle = $video->title;
...
<a class="evideo" href="<?php echo $youtubeEmbedLink; ?>" title="<?php echo $youtubeTitle; ?>">          <!-- (i) attribute -->
    <img src="<?php echo $youtubeThumbs; ?>" alt="<?php echo str_replace('"', '', $youtubeTitle); ?>" ... />  <!-- (ii) attribute, partial -->
</a>
<a class="h6 evideo" href="<?php echo $youtubeEmbedLink; ?>" title="<?php echo $youtubeTitle; ?>">       <!-- (iii) attribute -->
    <h2><?php echo $youtubeTitle; ?></h2>                                                              <!-- (iv) element body -->
</a>

Sites (i), (iii), and (iv) call no encoder. Site (ii) applies str_replace('"', '', $youtubeTitle) which strips quotes from one attribute and leaves the other three reflections untouched. The strongest sink is (iv) at line 60: a title containing <script>alert(2222)</script> produces <h2><script>alert(2222)</script></h2> in the rendered DOM, which the browser parses as a live script element and executes synchronously. The single half-mitigation at line 57 is the maintainer's evidence of awareness of the attribute-injection risk; the same developer left the other three sinks unprotected.

AVideo additionally caches the YouTube response for cacheTimeout seconds (default 3600), so even after the title is changed on YouTube or the video is removed, the AVideo gallery continues to serve the malicious title until the cache expires or is manually flushed.

Affected product: AVideo (WWBN), YouTubeAPI plugin
Tested version: master branch, commit 122b184 (snapshot dated 2026-05-22)

PoC

The AVideo operator must have the YouTubeAPI plugin enabled (the default after configuring a YouTube Data API key) with showGallerySection=true (the default). The attacker controls a YouTube video (uploaded under any free YouTube account) whose title is set to:

<script>alert(2222)</script>

The attacker arranges for the AVideo operator's configured YouTube search query (the keyword plugin setting, typically a channel name or topical phrase) to match the hostile video. The matching condition is the same as a normal YouTube search: a unique phrase in the video's description, a channel name the operator follows, or any query the operator has configured.

After AVideo's cacheTimeout window elapses (default 3600 seconds) and a fresh listVideos() call fetches the malicious title, any visitor opening the AVideo homepage triggers an alert(2222) modal dialog as the gallery card renders.

For deterministic test reproduction, deploy a mock YouTube Data API service that impersonates www.googleapis.com and youtube.googleapis.com on the AVideo Docker network and returns the malicious title directly. The PoC then reduces to:

https://avideo.example/

Configure the YouTubeAPI plugin in the admin panel (/plugins) with any non-empty developer_key and any keyword value, then load the homepage. The browser fires alert(2222) as the gallery section finishes rendering.

Impact

This is a Stored XSS vulnerability (CWE-79) in a publicly-rendered HTML context, with the data source under attacker control (CWE-829). Every visitor who loads any AVideo page rendering the YouTubeAPI gallery section is impacted: the injected JavaScript runs in the visitor's session under the AVideo origin, reads non-HttpOnly cookies, and issues authenticated requests as the visitor. When the visitor is an AVideo administrator, the injected JavaScript performs any admin action (create user, promote to admin, change configuration, install plugin) that uses cookie-based authentication without an additional CSRF token, escalating the bug into full administrative takeover. The payload persists for the duration of cacheTimeout (default 3600 seconds) after the malicious title is set on YouTube and survives YouTube removing the hostile video for the same window.