CVE-2026-113669: 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.assigns 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