Merge pull request #3 from Harrison-Wells-Cyber/codex/review-proxy-tool-for-internal-ad-environment

Change authentication method to better work in environments with tls inspection.

README.md

@@ -160,6 +160,25 @@ connections during high-concurrency tools such as NetExec; the default is 256. W
   but host telemetry, PowerShell logging, AMSI, EDR, crash dumps, or pagefile
   behavior are outside the loader's control.
 
+
+### TLS inspection / enterprise decryption
+
+If an authorized enterprise TLS inspection device presents a different leaf
+certificate to the Windows agent than the certificate loaded by the VPS server,
+agent certificate pinning will fail. The safest fix is to exempt the PS-Proxy
+server domain from TLS decryption so the agent sees the VPS certificate directly.
+
+For controlled labs where decryption cannot be bypassed, pass the inspected leaf
+certificate SHA-256 DER hash explicitly:
+
+```bash
+--agent-cert-pin-override <64-char-sha256-hex-pin>
+```
+
+Only use this when you control and trust the inspection device. This pins the
+agent to the certificate it actually sees, not the certificate file loaded by the
+VPS server.
+
 ## Current implementation status
 
 Implemented now:

cmd/psproxy-server/main.go

@@ -34,6 +34,7 @@ func main() {
 	port := flag.Int("port", 443, "TLS listener port")
 	cert := flag.String("cert", "", "TLS fullchain PEM; defaults to /etc/letsencrypt/live/<domain>/fullchain.pem")
 	key := flag.String("key", "", "TLS private key PEM; defaults to /etc/letsencrypt/live/<domain>/privkey.pem")
+	agentCertPinOverride := flag.String("agent-cert-pin-override", "", "override SHA-256 DER certificate pin embedded in staged agents; use only when an authorized TLS inspection device presents a different leaf cert")
 	tun := flag.String("tun", "psproxy0", "TUN interface name for the planned netstack data plane")
 	agentTemplate := flag.String("agent-template", "agent/loader/agent.ps1.tmpl", "PowerShell agent loader template")
 	agentAssemblyFile := flag.String("agent-assembly-b64-file", "", "file containing compressed/base64 PSProxy.Agent.dll; defaults to release/agent_assembly.b64 when present")
@@ -74,6 +75,13 @@ func main() {
 	if err != nil {
 		log.Fatalf("certificate pin failed: %v", err)
 	}
+	if *agentCertPinOverride != "" {
+		pin, err = normalizeCertPin(*agentCertPinOverride)
+		if err != nil {
+			log.Fatalf("invalid --agent-cert-pin-override: %v", err)
+		}
+		log.Printf("WARNING: using operator-supplied agent certificate pin override")
+	}
 	assembly, err := loadAssemblyB64(*agentAssemblyFile)
 	if err != nil {
 		log.Fatalf("agent assembly load failed: %v", err)
@@ -708,6 +716,17 @@ type multiFlag []string
 func (m *multiFlag) String() string     { return strings.Join(*m, ",") }
 func (m *multiFlag) Set(v string) error { *m = append(*m, v); return nil }
 
+func normalizeCertPin(pin string) (string, error) {
+	normalized := strings.ToLower(strings.ReplaceAll(strings.ReplaceAll(strings.TrimSpace(pin), ":", ""), " ", ""))
+	if len(normalized) != 64 {
+		return "", fmt.Errorf("pin must be 64 hex characters after removing colons/spaces")
+	}
+	if _, err := hex.DecodeString(normalized); err != nil {
+		return "", fmt.Errorf("pin must be hex: %w", err)
+	}
+	return normalized, nil
+}
+
 func certPin(path string) (string, error) {
 	pemBytes, err := os.ReadFile(path)
 	if err != nil {

cmd/psproxy-server/main_test.go

@@ -124,3 +124,23 @@ func TestSingleListenerAcceptReturnsEOFAfterFirstConn(t *testing.T) {
 		t.Fatal("second accept should return EOF")
 	}
 }
+
+func TestNormalizeCertPin(t *testing.T) {
+	pin := "BC:1D:96:47:91:A5:11:B4:95:26:EC:F2:25:35:37:F6:E6:17:0A:1A:19:4F:45:65:9E:88:0C:A7:A4:3D:6C:02"
+	got, err := normalizeCertPin(pin)
+	if err != nil {
+		t.Fatalf("normalize pin failed: %v", err)
+	}
+	want := "bc1d964791a511b49526ecf2253537f6e6170a1a194f45659e880ca7a43d6c02"
+	if got != want {
+		t.Fatalf("unexpected normalized pin: %s", got)
+	}
+}
+
+func TestNormalizeCertPinRejectsInvalidPins(t *testing.T) {
+	for _, pin := range []string{"abc", "zz1d964791a511b49526ecf2253537f6e6170a1a194f45659e880ca7a43d6c02"} {
+		if _, err := normalizeCertPin(pin); err == nil {
+			t.Fatalf("expected invalid pin %q to fail", pin)
+		}
+	}
+}