CVE-2026-63188

Logto is the modern, open-source auth infrastructure for SaaS and AI apps. Prior to 0.3.9, the Logto Tunnel npm package enabled createStaticFileProxy from packages/tunnel/src/commands/tunnel/index.ts and passed request.url from static asset requests through packages/tunnel/src/commands/tunnel/utils.ts using path.join(staticPath, request.url) and then fs.open(requestPath, "r") without URL normalization or a containment check. When --experience-path was enabled and the tunnel port was reachable, an unauthenticated requester could send a path containing ../ to createStaticFileProxy and read files outside the configured static directory that were readable by the logto-tunnel process. The service used server.listen(port), which could expose the tunnel to other hosts depending on the platform and deployment. This issue is fixed in version 0.3.9.

Logto is the modern, open-source auth infrastructure for SaaS and AI apps. Prior to 0.3.9, the Logto Tunnel npm package enabled createStaticFileProxy from packages/tunnel/src/commands/tunnel/index.ts and passed request.url from static asset requests through packages/tunnel/src/commands/tunnel/utils.ts using path.join(staticPath, request.url) and then fs.open(requestPath, "r") without URL normalization or a containment check. When --experience-path was enabled and the tunnel port was reachable, an unauthenticated requester could send a path containing ../ to createStaticFileProxy and read files outside the configured static directory that were readable by the logto-tunnel process. The service used server.listen(port), which could expose the tunnel to other hosts depending on the platform and deployment. This issue is fixed in version 0.3.9.

Summary

@logto/tunnel serves custom sign-in experience files from the --experience-path directory. When the tunnel service is reachable, a requester can use ../ path segments in a static asset request to read files outside that directory that the CLI process can read.

Details

The tunnel command accepts --experience-path as the local folder path for custom sign-in experience assets. packages/tunnel/src/commands/tunnel/index.ts enables createStaticFileProxy(path) when that option is set and sends non-Logto, non---experience-uri requests to that static proxy. The server is started with server.listen(port).

packages/tunnel/src/commands/tunnel/utils.ts builds the filesystem path as path.join(staticPath, fallBackToIndex ? index : request.url). For file asset paths, request.url is used directly. A request URL such as /../secret.txt resolves outside staticPath and is then opened with fs.open(requestPath, 'r'). There is no URL normalization and no containment check that the resolved path remains under the configured static directory before the file is read and returned.

The proof boundary is the packaged CLI end-to-end run. The filesystem read primitive was validated with equivalent Node HTTP handling for the affected code path, including that Node preserves /../secret.txt in request.url and that bare server.listen(port) binds to all interfaces on this platform.

PoC

1. Create a custom UI directory at /tmp/logto-ui/static with /tmp/logto-ui/static/index.html.
2. Create a sibling file outside the static root, for example /tmp/logto-ui/secret.txt.
3. Start the tunnel with logto-tunnel --endpoint https://<tenant-id>.logto.app --port 9000 --experience-path /tmp/logto-ui/static.
4. Request http://<host>:9000/../secret.txt.
5. The response body contains the contents of /tmp/logto-ui/secret.txt.

Impact

The observed result is arbitrary file read outside the configured custom UI static directory. If the tunnel port is reachable from another host, an unauthenticated network peer can read local files readable by the logto-tunnel process, including development secrets or credentials stored near the custom UI project.

Logto is the modern, open-source auth infrastructure for SaaS and AI apps. Prior to 0.3.9, the Logto Tunnel npm package enabled createStaticFileProxy from packages/tunnel/src/commands/tunnel/index.ts and passed request.url from static asset requests through packages/tunnel/src/commands/tunnel/utils.ts using path.join(staticPath, request.url) and then fs.open(requestPath, "r") without URL normalization or a containment check. When --experience-path was enabled and the tunnel port was reachable, an unauthenticated requester could send a path containing ../ to createStaticFileProxy and read files outside the configured static directory that were readable by the logto-tunnel process. The service used server.listen(port), which could expose the tunnel to other hosts depending on the platform and deployment. This issue is fixed in version 0.3.9.

Logto is the modern, open-source auth infrastructure for SaaS and AI apps. Prior to 0.3.9, the Logto Tunnel npm package enabled createStaticFileProxy from packages/tunnel/src/commands/tunnel/index.ts and passed request.url from static asset requests through packages/tunnel/src/commands/tunnel/utils.ts using path.join(staticPath, request.url) and then fs.open(requestPath, "r") without URL normalization or a containment check. When --experience-path was enabled and the tunnel port was reachable, an unauthenticated requester could send a path containing ../ to createStaticFileProxy and read files outside the configured static directory that were readable by the logto-tunnel process. The service used server.listen(port), which could expose the tunnel to other hosts depending on the platform and deployment. This issue is fixed in version 0.3.9.

Summary

@logto/tunnel serves custom sign-in experience files from the --experience-path directory. When the tunnel service is reachable, a requester can use ../ path segments in a static asset request to read files outside that directory that the CLI process can read.

Details

The tunnel command accepts --experience-path as the local folder path for custom sign-in experience assets. packages/tunnel/src/commands/tunnel/index.ts enables createStaticFileProxy(path) when that option is set and sends non-Logto, non---experience-uri requests to that static proxy. The server is started with server.listen(port).

packages/tunnel/src/commands/tunnel/utils.ts builds the filesystem path as path.join(staticPath, fallBackToIndex ? index : request.url). For file asset paths, request.url is used directly. A request URL such as /../secret.txt resolves outside staticPath and is then opened with fs.open(requestPath, 'r'). There is no URL normalization and no containment check that the resolved path remains under the configured static directory before the file is read and returned.

The proof boundary is the packaged CLI end-to-end run. The filesystem read primitive was validated with equivalent Node HTTP handling for the affected code path, including that Node preserves /../secret.txt in request.url and that bare server.listen(port) binds to all interfaces on this platform.

PoC

1. Create a custom UI directory at /tmp/logto-ui/static with /tmp/logto-ui/static/index.html.
2. Create a sibling file outside the static root, for example /tmp/logto-ui/secret.txt.
3. Start the tunnel with logto-tunnel --endpoint https://<tenant-id>.logto.app --port 9000 --experience-path /tmp/logto-ui/static.
4. Request http://<host>:9000/../secret.txt.
5. The response body contains the contents of /tmp/logto-ui/secret.txt.

Impact

The observed result is arbitrary file read outside the configured custom UI static directory. If the tunnel port is reachable from another host, an unauthenticated network peer can read local files readable by the logto-tunnel process, including development secrets or credentials stored near the custom UI project.