credentials.go

package adauth

import (
	"bytes"
	"context"
	"crypto/ecdsa"
	"crypto/ed25519"
	"crypto/rsa"
	"crypto/x509"
	"fmt"
	"net"
	"os"
	"strings"
	"time"

	"github.com/RedTeamPentesting/adauth/x509ext"
	"github.com/jcmturner/gokrb5/v8/config"
	"github.com/jcmturner/gokrb5/v8/iana/etypeID"
	"software.sslmate.com/src/go-pkcs12"
)

// Credential represents Active Directory credentials.
type Credential struct {
	// Username is the username without the domain.
	Username string
	// Password contains the users cleartext password if available.
	Password string
	// Domain holds the user's domain.
	Domain string
	// NTHash holds the user's NT hash or Kerberos RC4 key if available.
	NTHash string
	// AESKey holds the user's Kerberos AES128 or AES256 key if available.
	AESKey string
	// CCache contains the path to the user's CCache file.
	CCache string
	// ClientCert holds a client certificate for Kerberos or LDAP authentication if available.
	ClientCert *x509.Certificate
	// ClientCertKey holds the private key that corresponds to ClientCert.
	ClientCertKey any
	// CACerts holds CA certificates that were loaded alongside the ClientCert.
	CACerts []*x509.Certificate
	dc      string
	// PasswordIsEmptyString is true when an empty Password field should not be
	// interpreted as a missing password but as a password that happens to be
	// empty.
	PasswordIsEmtpyString bool
	// CCacheIsFromEnv indicates whether the CCache was set explicitly or
	// implicitly through an environment variable.
	CCacheIsFromEnv bool

	// Resolver can be used to set an alternative DNS resolver. If empty,
	// net.DefaultResolver is used.
	Resolver Resolver
}

// CredentialFromPFX creates a Credential structure for certificate-based
// authentication based on a PFX file.
func CredentialFromPFX(
	username string, domain string, pfxFile string, pfxPassword string,
) (*Credential, error) {
	pfxData, err := os.ReadFile(pfxFile)
	if err != nil {
		return nil, fmt.Errorf("read PFX: %w", err)
	}

	return CredentialFromPFXBytes(username, domain, pfxData, pfxPassword)
}

// CredentialFromPFX creates a Credential structure for certificate-based
// authentication based on PFX data.
func CredentialFromPFXBytes(
	username string, domain string, pfxData []byte, pfxPassword string,
) (*Credential, error) {
	cred := &Credential{
		Username: username,
		Domain:   domain,
	}

	key, cert, caCerts, err := DecodePFX(pfxData, pfxPassword)
	if err != nil {
		return nil, fmt.Errorf("decode PFX: %w", err)
	}

	rsaKey, ok := key.(*rsa.PrivateKey)
	if !ok {
		return nil, fmt.Errorf("PFX key is not an RSA private key but %T", rsaKey)
	}

	cred.ClientCert = cert
	cred.ClientCertKey = rsaKey
	cred.CACerts = caCerts

	user, domain, err := x509ext.UserAndDomainFromOtherNames(cert)
	if err == nil {
		if cred.Username == "" {
			cred.Username = user
		}

		if cred.Domain == "" {
			cred.Domain = domain
		}
	}

	return cred, nil
}

// UPN is the user principal name (username@domain). If the credential does not
// contain a domain, only the username is returned. If username and domain are
// empty, the UPN will be empty, too.
func (c *Credential) UPN() string {
	switch {
	case c.Username == "" && c.Domain == "":
		return ""
	case c.Domain == "":
		return c.Username
	default:
		return c.Username + "@" + c.Domain
	}
}

// LogonName is the legacy logon name (domain\username).
func (c *Credential) LogonName() string {
	return c.Domain + `\` + c.Username
}

// LogonNameWithUpperCaseDomain is like LogonName with the domain capitalized
// for compatibility with the Kerberos library (DOMAIN\username).
func (c *Credential) LogonNameWithUpperCaseDomain() string {
	return strings.ToUpper(c.Domain) + `\` + c.Username
}

// ImpacketLogonName is the Impacket-style logon name (domain/username).
func (c *Credential) ImpacketLogonName() string {
	return c.Domain + "/" + c.Username
}

// SetDC configures a specific domain controller for this credential.
func (c *Credential) SetDC(dc string) {
	c.dc = dc
}

// DC returns the domain controller of the credential's domain as a target.
func (c *Credential) DC(ctx context.Context, protocol string) (*Target, error) {
	if c.dc != "" {
		return newTarget(protocol, c.dc, true, c.CCache, c.Resolver), nil
	}

	if c.Domain == "" {
		return nil, fmt.Errorf("domain unknown")
	}

	_, addrs, err := ensureResolver(c.Resolver, nil).LookupSRV(ctx, "kerberos", "tcp", c.Domain)
	if err != nil {
		return nil, fmt.Errorf("lookup %q service of domain %q: %w", "kerberos", c.Domain, err)
	}

	if len(addrs) == 0 {
		return nil, fmt.Errorf("no %q services were discovered for domain %q", "kerberos", c.Domain)
	}

	return newTarget(protocol, strings.TrimRight(addrs[0].Target, "."), true, c.CCache, c.Resolver), nil
}

func (c *Credential) mustUseKerberos() bool {
	return c.Password == "" && c.NTHash == "" && (c.CCache != "" || c.AESKey != "")
}

// KerberosConfig returns the Kerberos configuration for the credential's
// domain. For compatibility with other Kerberos libraries, see the `compat`
// package.
func (c *Credential) KerberosConfig(ctx context.Context) (*config.Config, error) {
	dc, err := c.DC(ctx, "krbtgt")
	if err != nil {
		return nil, fmt.Errorf("find DC: %w", err)
	}

	krbConf := config.New()
	krbConf.LibDefaults.DefaultRealm = strings.ToUpper(c.Domain)
	krbConf.LibDefaults.AllowWeakCrypto = true
	krbConf.LibDefaults.DNSLookupRealm = false
	krbConf.LibDefaults.DNSLookupKDC = false
	krbConf.LibDefaults.TicketLifetime = time.Duration(24) * time.Hour
	krbConf.LibDefaults.RenewLifetime = time.Duration(24*7) * time.Hour
	krbConf.LibDefaults.Forwardable = true
	krbConf.LibDefaults.Proxiable = true
	krbConf.LibDefaults.RDNS = false
	krbConf.LibDefaults.UDPPreferenceLimit = 1 // Force use of tcp

	if c.NTHash != "" {
		// use RC4 for pre-auth but AES256 for ephemeral keys, otherwise we get
		// unsupported GSSAPI tokens during LDAP SASL handshake
		krbConf.LibDefaults.DefaultTGSEnctypeIDs = []int32{etypeID.AES256_CTS_HMAC_SHA1_96}
		krbConf.LibDefaults.DefaultTktEnctypeIDs = []int32{etypeID.RC4_HMAC}
		krbConf.LibDefaults.PermittedEnctypeIDs = []int32{etypeID.AES256_CTS_HMAC_SHA1_96}
		krbConf.LibDefaults.PreferredPreauthTypes = []int{int(etypeID.RC4_HMAC)}
	} else {
		krbConf.LibDefaults.DefaultTGSEnctypeIDs = []int32{
			etypeID.AES256_CTS_HMAC_SHA1_96, etypeID.AES128_CTS_HMAC_SHA1_96, etypeID.RC4_HMAC,
		}
		krbConf.LibDefaults.DefaultTktEnctypeIDs = []int32{
			etypeID.AES256_CTS_HMAC_SHA1_96, etypeID.AES128_CTS_HMAC_SHA1_96, etypeID.RC4_HMAC,
		}
		krbConf.LibDefaults.PermittedEnctypeIDs = []int32{
			etypeID.AES256_CTS_HMAC_SHA1_96, etypeID.AES128_CTS_HMAC_SHA1_96, etypeID.RC4_HMAC,
		}
		krbConf.LibDefaults.PreferredPreauthTypes = []int{
			int(etypeID.AES256_CTS_HMAC_SHA1_96), int(etypeID.AES128_CTS_HMAC_SHA1_96), int(etypeID.RC4_HMAC),
		}
	}

	krbConf.Realms = []config.Realm{
		{
			Realm:         strings.ToUpper(c.Domain),
			DefaultDomain: strings.ToUpper(c.Domain),
			AdminServer:   []string{dc.AddressWithoutPort()},
			KDC:           []string{net.JoinHostPort(dc.AddressWithoutPort(), "88")},
			KPasswdServer: []string{net.JoinHostPort(dc.AddressWithoutPort(), "464")},
			MasterKDC:     []string{dc.AddressWithoutPort()},
		},
		{
			Realm:         c.Domain,
			DefaultDomain: c.Domain,
			AdminServer:   []string{dc.AddressWithoutPort()},
			KDC:           []string{net.JoinHostPort(dc.AddressWithoutPort(), "88")},
			KPasswdServer: []string{net.JoinHostPort(dc.AddressWithoutPort(), "464")},
			MasterKDC:     []string{dc.AddressWithoutPort()},
		},
	}
	krbConf.DomainRealm = map[string]string{
		"." + c.Domain: strings.ToUpper(c.Domain),
		c.Domain:       strings.ToUpper(c.Domain),
	}

	return krbConf, nil
}

func splitUserIntoDomainAndUsername(user string) (domain string, username string) {
	switch {
	case strings.Contains(user, "@"):
		parts := strings.Split(user, "@")
		if len(parts) == 2 {
			return parts[1], parts[0]
		}

		return "", user
	case strings.Contains(user, `\`):
		parts := strings.Split(user, `\`)
		if len(parts) == 2 {
			return parts[0], parts[1]
		}

		return "", user
	case strings.Contains(user, "/"):
		parts := strings.Split(user, "/")
		if len(parts) == 2 {
			return parts[0], parts[1]
		}

		return "", user
	default:
		return "", user
	}
}

// DecodePFX loads the private key, certificate and certificate chain from PFX
// bytes that may or may not be protected by a password.
func DecodePFX(pfxData []byte, password string) (privateKey any, cert *x509.Certificate, chain []*x509.Certificate, err error) {
	// In some PFXs, especially those create by Microsoft tools, the cert and
	// chain order is reversed such that pkcs12.DecodeChain returns the CA cert
	// as "cert" and the leaf certificate in the chain (see
	// https://github.com/SSLMate/go-pkcs12/issues/54). Our strategy is that we
	// swap certifiates such that "cert" is the certificate that belongs to the
	// private key and "chain" contains all other certificates.
	privateKey, cert, chain, err = pkcs12.DecodeChain(pfxData, password)
	if err != nil || certMatchesKey(privateKey, cert) {
		return privateKey, cert, chain, err
	}

	for i := range chain {
		if !certMatchesKey(privateKey, chain[i]) {
			continue
		}

		newCert := chain[i]
		chain[i] = cert

		return privateKey, newCert, chain, nil
	}

	return privateKey, cert, chain, fmt.Errorf("private key does not match any of the %d certificates in PFX", len(chain)+1)
}

func certMatchesKey(key any, cert *x509.Certificate) bool {
	switch pub := cert.PublicKey.(type) {
	case *rsa.PublicKey:
		priv, ok := key.(*rsa.PrivateKey)
		if !ok {
			return false
		}

		if pub.N.Cmp(priv.N) != 0 {
			return false
		}

		return true
	case *ecdsa.PublicKey:
		priv, ok := key.(*ecdsa.PrivateKey)
		if !ok {
			return false
		}

		if pub.X.Cmp(priv.X) != 0 || pub.Y.Cmp(priv.Y) != 0 {
			return false
		}

		return true
	case ed25519.PublicKey:
		priv, ok := key.(ed25519.PrivateKey)
		if !ok {
			return false
		}

		privPublicKey, ok := priv.Public().(ed25519.PublicKey)
		if !ok {
			return false
		}

		if !bytes.Equal(privPublicKey, pub) {
			return false
		}

		return true
	default:
		return false
	}
}