Sentry Next.js SDK CVE-2026-114139

All of the following must hold simultaneously: (1) a tunnelRoute is configured in @sentry/nextjs; (2) the app is built with webpack (not Turbopack), which activates the vulnerable middleware-skip logic; (3) an application route directly collides with the tunnel path, or a root-level dynamic segment resolves under it; and (4) middleware is the only authorization control protecting that route. The vulnerable code skipped middleware for every path under tunnelRoute, whereas the actual tunnel rewrite serves only the exact tunnel path with valid numeric o and p query parameters on a POST request. Limiting factors: these are non-default, configuration-dependent conditions; apps that enforce authorization at the route/handler layer (not solely in middleware), that do not set tunnelRoute, or that build with Turbopack are not exposed.

This is a genuine authorization-bypass (CWE-693, Protection Mechanism Failure) in the @sentry/nextjs webpack integration, and the CVSS 4.0 vector (AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H) correctly frames it as a network-reachable, unauthenticated flaw with high confidentiality and integrity impact - hence the 9.1 score. However, the single most important signal is AT:P (Attack Requirements: Present): exploitation is gated behind a conjunction of non-default conditions, which materially lowers real-world risk below what the 9.1 headline suggests. No EPSS score, KEV listing, or public POC was provided, so there is no public exploit identified at time of analysis and no evidence of active exploitation; the vendor-published GitHub Security Advisory (GHSA-mchm-gjx6-7h55) and fix commits are the primary evidence. The 'Information Disclosure' tag understates the issue - the integrity impact (VI:H) means an attacker can reach protected routes to perform actions, not merely read data. Net: treat as a high-priority patch for the narrow population of apps that match the preconditions (tunnelRoute + webpack + a colliding route where middleware is the only authz control), but it is not a mass-exploitable, default-configuration flaw.

A Next.js app uses @sentry/nextjs with a configured tunnelRoute and a webpack build, and relies on middleware as its only authorization gate. An unauthenticated attacker sends a request to an application route that collides with the tunnel path (or a root dynamic segment resolving under it); the Sentry webpack integration skips middleware for that path, so the request reaches the protected route without authorization. No public exploit code was identified at time of analysis.