projectdiscovery/nuclei · info

not a mssql service

Error message

not a mssql service

What it means

Internal probe-result error from the mssql fingerprint helper. errNotMssql marks a TCP probe that completed (connection and reply received) but whose bytes are not a valid TDS pre-login reply. By design IsMssql() maps it to (false, nil) — 'probe finished, service is not MSSQL' — while FingerprintMssql() surfaces it as a Go error to the caller.

Source

Thrown at pkg/js/libs/mssql/fingerprint.go:19

package mssql

import (
	"context"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"net"
	"time"

	"github.com/projectdiscovery/nuclei/v3/pkg/protocols/common/protocolstate"
)

// errNotMssql marks a completed probe whose response is not a valid MSSQL
// pre-login reply. IsMssql maps this to (false, nil); FingerprintMssql still
// surfaces it as an error.
var errNotMssql = errors.New("not a mssql service")

const (
	mssqlFingerprintTimeout = 5 * time.Second

	tdsTypeTabularResult = 0x04
	tdsStatusEOM         = 0x01
	tdsTerminator        = 0xff

	plTokenVersion    = 0x00
	plTokenEncryption = 0x01
	plTokenInstOpt    = 0x02
	plTokenThreadID   = 0x03
	plTokenMars       = 0x04
	plTokenTraceID    = 0x05

	encryptOff    = 0x00
	encryptOn     = 0x01
	encryptNotSup = 0x02

View on GitHub (pinned to 265b3a3dec)

Solutions

1. Use IsMssql instead of FingerprintMssql when a boolean verdict without an error is wanted
2. Treat this error from FingerprintMssql as 'not MSSQL' rather than a failure of the probe itself
3. Only run the mssql helper against ports you expect to speak TDS

Example fix

// before
fp, err := mssql.FingerprintMssql(host, port)
if err != nil { return err }
// after
fp, err := mssql.FingerprintMssql(host, port)
if errors.Is(err, mssql.ErrNotMssql) { return nil } // not mssql, not a failure

func isNotMssql(err error) bool { return errors.Is(err, mssql.ErrNotMssql) }

isMssql, err := mssql.IsMssql(host, port) // preferred: never errors for non-mssql
if err != nil { // transport-level failure, distinct from 'not mssql'
    log.Debugf("mssql probe %s:%d: %v", host, port, err)
}
// or with FingerprintMssql:
fp, err := mssql.FingerprintMssql(host, port)
if errors.Is(err, mssql.ErrNotMssql) { /* verdict: service is not mssql */ }

When it happens

Trigger: Calling FingerprintMssql on a port running MySQL, PostgreSQL, SMB, or any non-TDS service; calling IsMssql on the same ports returns false with no error.

Common situations: Scanning mixed-service ports (3306, 5432, 445) with the mssql network helper; port 1433 redirected to another protocol.

Related errors

• %w: invalid TDS packet length %d
• %w: %v
• unexpected TDS type 0x%02x
• unexpected TDS status 0x%02x
• invalid host or port

AI-assisted analysis of projectdiscovery/nuclei@265b3a3dec (2026-08-15). Data as JSON: /api/errors/8e0048eaa37e6125. Report an issue: GitHub.