LaunchServer FileServerHandler has an unauthenticated path traversal issue

Summary

An unauthenticated path traversal in the LaunchServer HTTP file server (FileServerHandler) lets any remote actor read any file readable by the LaunchServer process (e.g. ../../../../etc/passwd). This is a generic arbitrary-file-read primitive, so the fix must address the traversal itself, not any specific file.

The readable files include the server's own secrets, which turns this from information disclosure into full compromise: the ECDSA private key that signs access JWTs (.keys/ecdsa_id), the refresh-token salt (.keys/legacySalt), and LaunchServer.json (database credentials). With the signing key an attacker mints a valid access token for any account, including admins. That is a full authentication bypass. Pre-auth, default config, port 9274.

Affected: GravitLauncher LaunchServer ≤ 5.7.11 (the LaunchServer application; the published pro.gravit.launcher:*-api Maven artifacts do not contain the vulnerable code).

Details

In FileServerHandler.channelRead0:

path = Paths.get(IOHelper.getPathFromUrlFragment(uri)).normalize().toString().substring(1); // line 194
File file = base.resolve(path).toFile();                                                     // line 200 - no second normalize()

substring(1) blindly strips a leading slash, assuming the request-target always starts with /. Netty's HttpServerCodec accepts a request-target without a leading slash verbatim (decoderResult().isSuccess() == true). For such a target, normalize() cannot collapse the leading .., substring(1) turns ../ into ./ (leaving the remaining ..), and base.resolve(path), which is not re-normalized, resolves outside updatesDir.

file.isHidden() (line 201) is checked only on the final path component, so targets that don't start with a dot (ecdsa_id, rsa_id, legacySalt, LaunchServer.json) are served even with showHiddenFiles=false.

The file server is enabled by default (netty.fileServerEnabled=true) and bound to 0.0.0.0:9274. No auth handler precedes FileServerHandler; WebSocketServerProtocolHandler("/api") forwards non-WebSocket / non-/api requests down to it, so the attack is a plain HTTP GET (no WebSocket).

PoC

Reproduced on a from-source build of v5.7.11 (Netty 4.2.12).
Must use a raw socket. curl/browsers/HTTP libraries normalize the path and prepend /, hitting the safe branch (false "not reproducible").

printf 'GET ../../.keys/ecdsa_id HTTP/1.1\r\nHost: x\r\n\r\n' | nc <host> 9274

Returns the raw ECDSA private-key bytes. Same for ../../.keys/rsa_id, ../../.keys/legacySalt, ../../LaunchServer.json. %2e%2e/... (no leading slash) also works. Depth-robust arbitrary read: ../../../../../../etc/passwd.
Control (confirms the root cause): GET /../../.keys/ecdsa_id (WITH leading slash) → 404. Only the no-leading-slash form escapes.

Impact

Unauthenticated remote read of any file the process can access. What that exposes:
- .keys/ecdsa_id: the key that signs access JWTs. With it, an attacker mints a valid token for any account, including admins, so this is a full authentication bypass.
- .keys/legacySalt: lets an attacker forge refresh tokens.
- LaunchServer.json: database credentials.
- Any other file readable by the process (config, logs, system files).

Deployment note: a normalizing L7 reverse proxy (stock nginx location / { proxy_pass ...; }) rejects the no-leading-slash request (400) and collapses leading-slash traversal, blocking the primary vector. But the default bind is 0.0.0.0:9274, so protection relies on firewalling the backend port; L4/TCP proxies (HAProxy TCP, nginx stream, CF Spectrum) and direct exposure remain exploitable.

Suggested fix

1. Re-normalize() after base.resolve(path) and verify resolved.startsWith(base).
2. Reject request-targets that don't start with / (400).
3. Default-bind to 127.0.0.1; store .keys outside updatesDir.