YesWiki Vulnerable to Authenticated PHP Object Injection in BazarImportAction via unserialize

Details

Sink

tools/bazar/services/CSVManager.php line 372-399:

public function importEntry(array $importedEntries, string $formId): ?array
{
    if (!$this->importdone) {
        // ...
        foreach ($importedEntries as $entry) {
            $entry = unserialize(base64_decode($entry));   // <-- SINK
            $entry = array_map('strval', $entry);
            // ...

There is no ['allowed_classes' => false] argument; arbitrary classes are instantiated. The subsequent array_map('strval', $entry) additionally exercises __toString on each top-level array element, doubling the magic-method surface available to a gadget chain.

Source

tools/bazar/actions/BazarImportAction.php:

// formatArguments()
'mode' => (isset($_POST['submit_file']) && !empty($_FILES['fileimport']['name'])) ? 'submitfile' :
    (isset($_POST['importfiche']) ? 'importentries' : 'default'),
'importentries' => $_POST['importfiche'] ?? null,

// run()
case 'importentries':
    // ...
    $importedEntries = $this->CSVManager->importEntry($this->arguments['importentries'], $vID['id']);
    break;

$_POST['importfiche'] flows directly to the sink. The mode switches to 'importentries' whenever the request body contains the key, so an attacker need only POST importfiche[0]=<payload>.

Reachability

1. The action is registered as bazarimport. The default BazaR page (setup/sql/default-content.sql -> BazaR page entry, ships with {{bazar showexportbuttons="1"}}) routes ?BazaR&vue=importer&id_typeannonce=<N> to BazarAction::run() -> case VOIR_IMPORTER -> callAction('bazarimport', ...) (tools/bazar/actions/BazarAction.php:257-258). So the sink is reachable on a default install with no extra page authoring.

2. BazarImportAction::run() calls $this->checkSecuredACL() with the default $adminOnly=true. Only wiki admins (or accounts the admin has added to the bazarimport action ACL) can execute it.

3. The importentries branch does NOT invoke CsrfTokenController::checkToken(...). Grepping tools/bazar/actions/BazarImportAction.php confirms the action class has no csrf or checkToken reference at all. This is asymmetric with sibling actions: tools/bazar/controllers/FormController.php does call checkToken('main', 'POST', 'confirmDeleteToken') for destructive operations. The import path skips the same protection.

4. Therefore the full kill chain for a remote attacker is:

a. Identify any admin user on the target wiki.
b. Deliver an HTML page (email, chat, link) that auto-POSTs importfiche[0]=<base64-encoded PHPGGC payload> to https://<wiki>/?BazaR&vue=importer&id_typeannonce=1.
c. The admin's session cookie is sent automatically; the action passes checkSecuredACL; the unserialize fires.

Gadget chain availability

composer.json requires doctrine/annotations ^1.11 and doctrine/cache ^1.10. Both have published PHPGGC chains (Doctrine/RCE1, Doctrine/FW1, Doctrine/FW2, etc., from https://github.com/ambionics/phpggc). These chains terminate in either system($cmd) (RCE1) or file_put_contents($php_file, $contents) (FW1) entry-points -- both sufficient to give the attacker shell on the YesWiki host.

This advisory does not include a working PHPGGC chain end-to-end (writing a chain that survives YesWiki's exact dependency-resolved class graph is separate work). The PoC demonstrates the primitive (attacker-controlled class instantiation + magic-method execution); the chain is a downstream exercise using public tooling.

Past advisories cross-check

YesWiki's published GitHub advisories cover XSS, SQLi, arbitrary-PHP-file-write RCE, path traversal, and unauthenticated backup download. None covers an unserialize / PHP-object-injection sink, so this is a novel vulnerability class for the project.

PoC

A self-contained PoC reproducing the inner loop is available; it copies the exact two-line sink and proves that attacker-controlled __destruct runs without booting the full application.

Run:

php poc.php

Output (verbatim):

Crafted importfiche[0] payload (form-ready, urlencoded):
YToxOntpOjA7Tzo2OiJHYWRnZXQiOjE6e3M6NjoibWFya2VyIjtzOjIyOiJQV05FRC1GUk9NLVVOU0VSSUFMSVpFIjt9fQ%3D%3D

== before importEntry ==
[Gadget] __destruct fired with marker='PWNED-FROM-UNSERIALIZE'
PHP Fatal error:  Uncaught Error: Object of class Gadget could not be converted to string ...
[Gadget] __destruct fired with marker='PWNED-FROM-UNSERIALIZE'

The two [Gadget] __destruct fired lines (one from inside the loop, one from the engine shutdown after the TypeError) confirm that the attacker-defined Gadget::__destruct executed -- with the attacker-supplied marker -- inside the unmodified importEntry code path.

End-to-end against a live YesWiki install:

curl -i -b "yeswiki_session=<admin_cookie>" \
     -X POST "https://wiki.example.com/?BazaR&vue=importer&id_typeannonce=1" \
     --data-urlencode \
     "importfiche[0]=YToxOntpOjA7Tzo2OiJHYWRnZXQiOjE6e3M6NjoibWFya2VyIjtzOjIyOiJQV05FRC1GUk9NLVVOU0VSSUFMSVpFIjt9fQ=="

(replace the payload with a real PHPGGC Doctrine/FW1 or Doctrine/RCE1 output to obtain RCE on the target host).

Impact

• Authenticated wiki admin who lands on attacker-controlled HTML obtains remote code execution on the YesWiki server (via the cross-site forgery path; no admin interaction with the import UI is required).
• An attacker who has already compromised an admin password upgrades from "wiki content management" to "OS shell on the hosting box".
• The compromise survives the wiki layer entirely: the attacker can write web shells, exfiltrate other sites on shared hosting, modify wakka.config.php, dump the MySQL database, and pivot from there.

Suggested fix

1. tools/bazar/services/CSVManager.php::importEntry -- pass ['allowed_classes' => false] to unserialize, or, better, replace the base64+serialize transport with the JSON transport the current UI already uses (?api/entries/{formId} POST in tools/bazar/presentation/javascripts/bazar-import.js). The serialized-PHP transport appears to be an unused legacy path.
2. tools/bazar/actions/BazarImportAction.php -- add a CsrfTokenController::checkToken('main', 'POST', 'csrf-token', false) guard for the 'importentries' mode (and any other state-changing modes). The existing tools/bazar/controllers/FormController.php pattern can be lifted directly.