projectdiscovery/nuclei · error

failed to send MS-TNAP login packet

Error message

failed to send MS-TNAP login packet: %w

What it means

Thrown by telnet.DetectNTLM when writing the crafted MS-TNAP login packet to the TCP connection fails. The dial itself succeeded (protocolstate dialer connected, a 10-second deadline was set), but the subsequent conn.Write of telnetmini.CreateTNAPLoginPacket() returned an error — the connection was broken between dial and write, typically a reset by the server or a middlebox.

Solutions

1. Verify the target actually speaks telnet on that port before calling DetectNTLM
2. Retry once — transient resets are common during scanning
3. Check local egress/firewall rules if every host fails at the write step

// confirm the port actually speaks telnet before the NTLM probe
// (e.g. banner check), then call DetectNTLM

let r = null; for (let i = 0; i < 2 && !r; i++) { try { r = client.DetectNTLM(host, port); } catch (e) { if (!String(e).includes('send MS-TNAP')) throw e; } }

When it happens

Trigger: Target accepts the TCP handshake but immediately resets non-telnet or suspicious traffic; a firewall/IPS dropping the MS-TNAP packet; the service closing the connection during protocol negotiation before this step; transient network failure mid-handshake.

Common situations: Scanning hosts where port 23 is forwarded to a non-telnet service; security devices resetting anomalous payloads; flaky links to distant targets.

Related errors

• no response received
• failed to parse NTLM response
• failed to read response
• authentication failed
• prompt not found (read cap reached)

AI-assisted analysis of projectdiscovery/nuclei@265b3a3dec (2026-08-15). Data as JSON: /api/errors/60be5ba4486d13d4. Report an issue: GitHub.

Appendix: source

Thrown at pkg/js/libs/telnet/telnet.go:253

	}()

	// Create telnet client using the telnetmini library
	client := telnetmini.New(conn)
	defer func() {
		_ = client.Close()
	}()

	// Set timeout
	_ = conn.SetDeadline(time.Now().Add(10 * time.Second))

	// Use the MS-TNAP packet crafting functions from our telnetmini library
	// Create MS-TNAP Login Packet (Option Command IS) as per Nmap script
	tnapLoginPacket := telnetmini.CreateTNAPLoginPacket()

	// Send the MS-TNAP login packet
	_, err = conn.Write(tnapLoginPacket)
	if err != nil {
		return nil, fmt.Errorf("failed to send MS-TNAP login packet: %w", err)
	}

	// Read response data
	buffer := make([]byte, 4096)
	n, err := conn.Read(buffer)
	if err != nil {
		return nil, fmt.Errorf("failed to read response: %w", err)
	}

	if n == 0 {
		return nil, fmt.Errorf("no response received")
	}

	// Parse NTLM response using our telnetmini library functions
	response := buffer[:n]

	// Use the parsing functions from our library instead of reimplementing
	// This should use the NTLM parsing functions we added to telnetmini

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