mirror of
https://github.com/mandiant/gopacket
synced 2026-06-21 13:57:02 +00:00
Jacob Paullus
8eea029431
The embedded gokrb5/v8 library hard-coded net.DialTimeout for AS/TGS
exchanges, bypassing -proxy and leaking the operator's source IP to the
KDC (UDP/88 first, TCP/88 fallback). The DCERPC Kerberos auth path used
a separate library (oiweiwei/gokrb5.fork/v9 via go-msrpc) that leaked the
same way.
Vendor jcmturner/gokrb5/v8 in-tree at pkg/third_party/gokrb5 with a
required KDCDialer first argument on every client constructor, so
proxy-bypass becomes a compile error. Wire kerberos.TransportKDCDialer
everywhere a gokrb5 client is built. Stamp udp_preference_limit=1 and
dns_lookup_kdc/realm=false unconditionally so KRB5 is TCP-only and the
OS resolver is never consulted; /etc/krb5.conf and $KRB5_CONFIG are
deliberately not read.
For DCERPC: set krbConfig.KDCDialer on every krb5.Config, pass
dcerpc.WithDialer(transport.ContextDialer{}) on every dcerpc.Dial, and
use the "ncacn_ip_tcp:" StringBinding prefix on the OXID-pivot dial so
go-msrpc's hard-coded pre-dial net.LookupIP is skipped (defers FQDN
resolution to the SOCKS5 proxy).
Verified against a live GOAD lab: 8 Kerberos-touching tools plus 5
NTLM/password/PtH regressions all operate through SOCKS5 with zero
direct packets to the AD subnet. Negative control (no -proxy)
immediately emits direct SYNs to the KDC, confirming both the leak
class and the fix.
89 lines
2.5 KiB
Go
89 lines
2.5 KiB
Go
// Copyright 2026 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package smb
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import (
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"encoding/asn1"
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"github.com/mandiant/gopacket/pkg/third_party/gokrb5/gssapi"
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"github.com/mandiant/gopacket/pkg/third_party/gokrb5/types"
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"github.com/mandiant/gopacket/pkg/kerberos"
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"github.com/mandiant/gopacket/pkg/third_party/smb2"
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)
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// OID for Kerberos V5
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var OIDKerberos = asn1.ObjectIdentifier{1, 2, 840, 113554, 1, 2, 2}
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type KerberosInitiator struct {
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KrbClient *kerberos.Client
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TargetSPN string
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sessionKey types.EncryptionKey // Full key including type for MIC calculation
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}
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func (k *KerberosInitiator) OID() asn1.ObjectIdentifier {
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return OIDKerberos
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}
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func (k *KerberosInitiator) InitSecContext() ([]byte, error) {
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// Generate AP-REQ with full key (includes encryption type)
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apReq, key, err := k.KrbClient.GenerateAPReqFull(k.TargetSPN)
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if err != nil {
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return nil, err
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}
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k.sessionKey = key
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return apReq, nil
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}
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func (k *KerberosInitiator) AcceptSecContext(sc []byte) ([]byte, error) {
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// Handle mutual auth response (AP-REP) if needed.
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// For SMB, we usually just succeed if we get here?
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// Real implementation should parse AP-REP and verify signature.
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return nil, nil
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}
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func (k *KerberosInitiator) Sum(b []byte) []byte {
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// GSS_GetMIC for Kerberos (RFC 4121)
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// This is used for SPNEGO mechListMIC during authentication
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if k.sessionKey.KeyValue == nil {
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return nil
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}
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// Create MIC token using gokrb5's GSSAPI support
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micToken, err := gssapi.NewInitiatorMICToken(b, k.sessionKey)
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if err != nil {
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return nil
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}
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micBytes, err := micToken.Marshal()
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if err != nil {
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return nil
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}
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return micBytes
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}
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func (k *KerberosInitiator) SessionKey() []byte {
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// SMB2 expects a 16-byte session key for signing/encryption
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// AES256 keys are 32 bytes, but SMB2 derives a 16-byte signing key from it
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if len(k.sessionKey.KeyValue) > 16 {
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return k.sessionKey.KeyValue[:16]
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}
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return k.sessionKey.KeyValue
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}
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// Verify compliance
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var _ smb2.Initiator = (*KerberosInitiator)(nil)
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