CVE-2026-34077

In React Router and Remix Run libraries, a vulnerability allows reading/writing session files outside the specified directory when using createFileSessionStorage() with an unsigned cookie. An attacker can cause the session to access locations outside the intended session file directory, depending on web server process permissions.

Vulnerability in React Router versions 7.0.0 through 7.17.0. Unauthenticated requests to the manifest endpoint can overload the server and slow down responses. This does not affect applications using Declarative Mode (<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>).

React Router versions 6.0.0 through 7.17.0 are vulnerable to Open Redirect through use of backslashes in <Link> and useNavigate. This issue has been fixed in version 7.18.0.

React Router versions 6.30.2 through 6.30.4 and 7.9.6 through 7.12.0 are vulnerable to XSS in applications that allow open redirects. An attacker could craft a malicious link that redirects users to an unexpected external site or exploits an XSS vector. This issue has been fixed in version 7.13.0.

React Router versions 7.11.0 through 7.17.0 are missing protocol validation in RSCErrorHandler, allowing redirects from untrusted sources. This only affects applications using unstable RSC APIs. Fixed in version 7.18.0.

React Router versions 6.4.0 through 7.17.0 allow unexpected constructor execution on the client if application code allows attacker-supplied input to overwrite certain aspects of SSR errors. This can trigger an outbound network request. Only affects Framework Mode and Data Mode applications performing manual SSR/hydration. Fixed in version 7.18.0.

React Router versions from 7.12.0 to 7.15.1 had insufficient CSRF checks in Framework Mode that operated on POST requests but were bypassed on PUT/PATCH/DELETE requests. This vulnerability is fixed in version 7.15.1.

React Router versions 7.0.0 through 7.14.x and @remix-run/server-runtime versions 2.10.0 through 2.17.4 contain a DoS vulnerability via unbounded path expansion in the __manifest endpoint. Attackers can send crafted requests that consume excessive server resources.

React Router versions 7.0.0 through 7.14.1 in Framework Mode can allow remote code execution (RCE) via external requests if the application has an existing prototype pollution vulnerability. Two-step attack. Does not affect Declarative or Data Mode.

React Router versions 7.0.0 through 7.14.0 and 6.7.0 through 6.30.3 contain an open redirect vulnerability where certain URLs passed to the redirect function can be reinterpreted as protocol-relative URLs, redirecting to an external domain.