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.
41 lines
844 B
Go
41 lines
844 B
Go
package rfc4757
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import (
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"bytes"
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"crypto/hmac"
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"crypto/md5"
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"io"
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)
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// Checksum returns a hash of the data in accordance with RFC 4757
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func Checksum(key []byte, usage uint32, data []byte) ([]byte, error) {
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// Create hashing key
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s := append([]byte(`signaturekey`), byte(0x00)) //includes zero octet at end
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mac := hmac.New(md5.New, key)
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mac.Write(s)
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Ksign := mac.Sum(nil)
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// Format data
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tb := UsageToMSMsgType(usage)
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p := append(tb, data...)
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h := md5.New()
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rb := bytes.NewReader(p)
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_, err := io.Copy(h, rb)
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if err != nil {
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return []byte{}, err
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}
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tmp := h.Sum(nil)
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// Generate HMAC
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mac = hmac.New(md5.New, Ksign)
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mac.Write(tmp)
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return mac.Sum(nil), nil
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}
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// HMAC returns a keyed MD5 checksum of the data
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func HMAC(key []byte, data []byte) []byte {
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mac := hmac.New(md5.New, key)
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mac.Write(data)
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return mac.Sum(nil)
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}
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