Summary
logto-tunnel serves files outside --experience-path via path traversal
@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
- Create a custom UI directory at
/tmp/logto-ui/staticwith/tmp/logto-ui/static/index.html. - Create a sibling file outside the static root, for example
/tmp/logto-ui/secret.txt. - Start the tunnel with
logto-tunnel --endpoint https://<tenant-id>.logto.app --port 9000 --experience-path /tmp/logto-ui/static. - Request
http://<host>:9000/../secret.txt. - 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.
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2026-63188? CVE-2026-63188 is a high-severity path traversal vulnerability in @logto/tunnel (npm), affecting versions <= 0.3.8. It is fixed in 0.3.9. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- Which versions of @logto/tunnel are affected by CVE-2026-63188? @logto/tunnel (npm) versions <= 0.3.8 is affected.
- Is there a fix for CVE-2026-63188? Yes. CVE-2026-63188 is fixed in 0.3.9. Upgrade to this version or later.
- Is CVE-2026-63188 exploitable, and should I be worried? Whether CVE-2026-63188 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-63188 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-63188? Upgrade
@logto/tunnelto 0.3.9 or later.