Hunt Ntlm Info Skill for Claude

Crown Jewel Targets

NTLM info disclosure is a Medium-severity finding when chained to context — the leak itself is intentional protocol behavior (RFC-compliant NTLMSSP challenge), but on internet-exposed enterprise infrastructure it provides exact reconnaissance for the next stage of an attack. Highest-value targets:

• Internet-reachable IIS / SharePoint / Exchange / OWA with dual-auth (Forms + NTLM, or NTLM + Kerberos)
• Citrix NetScaler / VMware Horizon View internet-facing gateways with NTLM-backed AD auth
• Lync / Skype for Business / Teams On-Prem edge servers
• WSUS / Windows Update Services with NTLM-protected admin paths
• CIFS-style fileshare proxies (HCL Sametime, IBM Notes Domino) that proxy NTLM
• Legacy SharePoint farms that left NTLM enabled on the public-zone IIS binding

What makes this pay:

• Internal AD domain disclosure (parent-forest mapping, e.g. customer.parent-corp.example → tenant inside corporate-AD tree)
• Default-Windows-hostname disclosure (WIN-XXXXXXXXXXX pattern signals rushed provisioning → likely default service-account passwords)
• Timestamp leak (used in NTLMv2 hash cracking acceleration)
• Direct attack-map enrichment for credential spraying combined with hunt-auth-bypass Legacy-Protocol Matrix

Attack Surface Signals

Response headers signaling NTLM availability:

WWW-Authenticate: NTLM
WWW-Authenticate: Negotiate
WWW-Authenticate: NTLM, Negotiate
WWW-Authenticate: Negotiate, NTLM

URL patterns where NTLM is commonly exposed:

/_api/web/CurrentUser                  (SharePoint REST)
/_vti_bin/*.asmx                       (SharePoint legacy SOAP)
/EWS/Exchange.asmx                     (Exchange Web Services)
/Autodiscover/Autodiscover.xml         (Exchange autodiscover)
/owa/                                  (Outlook Web App)
/Microsoft-Server-ActiveSync           (ActiveSync)
/PowerShell                            (Exchange Mgmt Shell over HTTPS)
/api/v3/                               (TeamCity, Atlassian)
/wsus/                                 (Windows Server Update Services)
/manager/html                          (some Tomcat behind IIS)
/iisstart.htm                          (default IIS, sometimes reveals NTLM upstream)

Tech-stack signals:

• IIS on the public internet (almost always NTLM-capable, even if Forms is the front)
• SharePoint Web Front End (almost always dual-auth Forms + NTLM)
• Exchange edge transport
• Server header Microsoft-HTTPAPI/2.0, Microsoft-IIS/*, IIS/*

Step-by-Step Hunting Methodology

• Probe every anonymous endpoint for WWW-Authenticate: NTLM. Send a vanilla GET and inspect response headers. If NTLM is offered, proceed.

• Send a valid NTLMSSP Type-1 message anonymously. The Type-1 base64 below requests NetBIOS-domain and Workstation info from the server:

   Authorization: NTLM TlRMTVNTUAABAAAAB4IIogAAAAAAAAAAAAAAAAAAAAAGAbEdAAAADw==

This is the standard test Type-1 with negotiate flags NTLMSSP_NEGOTIATE_UNICODE | NTLMSSP_NEGOTIATE_OEM | NTLMSSP_NEGOTIATE_NTLM | NTLMSSP_NEGOTIATE_ALWAYS_SIGN | NTLMSSP_NEGOTIATE_KEY_EXCH | NTLMSSP_NEGOTIATE_56 | NTLMSSP_NEGOTIATE_128 | NTLMSSP_NEGOTIATE_TARGET_INFO. The OS Version field (06 01 B1 1D 00 00 00 0F) is Windows 7 build 7601 — accepted by virtually every NTLM responder.

• Use a keep-alive raw socket, not Python requests / curl one-shot. Most HTTP libraries close the connection between the Type-1 send and Type-2 reception. Use one of:
• Burp Repeater with Connection: keep-alive set explicitly
• Burp mcp__burp__send_http1_request (handles keep-alive natively)
• Python raw socket + ssl.wrap_socket (see Payload section)

• Parse the Type-2 challenge from the WWW-Authenticate: NTLM <base64> response header. Base64-decode the value. The structure is NTLMSSP per MS-NLMP:
• Bytes 0-7: literal NTLMSSP\0
• Bytes 8-11: MessageType = \x02\x00\x00\x00
• Bytes 12-19: TargetName SecurityBuffer (len, alloc, offset)
• Bytes 20-23: NegotiateFlags
• Bytes 24-31: Server Challenge (8 bytes — useful for offline cracking)
• Bytes 40-47: TargetInfo SecurityBuffer (len, alloc, offset)
• TargetInfo body: AV_PAIRS array of (AvId u16, AvLen u16, Value)

• Decode the AV_PAIRS. The AvIds you care about:
• 1 = NetBIOS Computer Name
• 2 = NetBIOS Domain Name
• 3 = DNS Computer Name (FQDN of the responding server)
• 4 = DNS Domain Name (the AD domain)
• 5 = DNS Tree Name (the AD forest root)
• 7 = Timestamp (FILETIME, useful for NTLMv2 hash relay / cracking)
• 9 = Target Name (in newer NTLMSSP)

• Map findings to severity tier:
• Internet-exposed + default WIN-XXXXXXXXXXX hostname + corporate-AD-tree disclosure → Medium
• Internet-exposed + named-server hostname (SPWEB01.corp.example) + corporate-AD-tree → Low-Medium
• Intranet-only + any disclosure → Informational
• Combine with hunt-auth-bypass Legacy-Protocol Matrix findings on the same host → upgrade the auth-bypass finding's severity since the attacker has UPN/SAM format ready

• Check the timestamp. If AV[7] returns a current FILETIME within ~5s of Date: header, the system clock is synced — useful intel for Kerberos golden-ticket forging (out of bug-bounty scope but red-team relevant).

• Cross-reference with subdomain enum. The DNS Tree name often reveals the *parent forest* — e.g. customer.parent-corp.example reveals the customer is a sub-domain INSIDE corporate-parent AD, not a separate tenant. This is a privacy / topology-disclosure escalation that programs sometimes accept as Medium.

Payload & Detection Patterns

Generic NTLM Type-1 anonymous probe (curl + raw socket fallback):

# Most one-shot curl runs DON'T return Type-2 because the connection closes.
# Use this as a quick probe to confirm NTLM is offered:
curl -sk -I -H "Authorization: NTLM TlRMTVNTUAABAAAAB4IIogAAAAAAAAAAAAAAAAAAAAAGAbEdAAAADw==" \
  "https://target.example/_api/web/CurrentUser" 2>&1 | grep -i "WWW-Authenticate"

Burp send_http1_request (recommended for full Type-2 capture):

GET /_api/web/CurrentUser HTTP/1.1
Host: target.example
Authorization: NTLM TlRMTVNTUAABAAAAB4IIogAAAAAAAAAAAAAAAAAAAAAGAbEdAAAADw==
Connection: keep-alive
User-Agent: Mozilla/5.0

Python raw socket + AV_PAIR decoder:

import socket, ssl, base64, struct, re
from datetime import datetime, timezone

HOST = "target.example"
ctx = ssl.create_default_context()
ctx.check_hostname = False
ctx.verify_mode = ssl.CERT_NONE

s = ctx.wrap_socket(socket.create_connection((HOST, 443)), server_hostname=HOST)
s.sendall(
    f"GET /_api/web/CurrentUser HTTP/1.1\r\n"
    f"Host: {HOST}\r\n"
    "Authorization: NTLM TlRMTVNTUAABAAAAB4IIogAAAAAAAAAAAAAAAAAAAAAGAbEdAAAADw==\r\n"
    "User-Agent: Mozilla/5.0\r\nConnection: keep-alive\r\n\r\n".encode()
)
data = b""
while True:
    chunk = s.recv(8192)
    if not chunk: break
    data += chunk
    if b"\r\n\r\n" in data: break

m = re.search(rb"WWW-Authenticate:\s*NTLM\s+([A-Za-z0-9+/=]{20,})", data, re.I)
if m:
    b = base64.b64decode(m.group(1).decode("ascii"))
    assert b[:8] == b"NTLMSSP\x00"
    tn_len, _, tn_off = struct.unpack_from('<HHI', b, 12)
    ti_len, _, ti_off = struct.unpack_from('<HHI', b, 40)
    print(f"TargetName: {b[tn_off:tn_off+tn_len].decode('utf-16-le', errors='ignore')!r}")
    av_types = {1:'NetBIOS Computer Name', 2:'NetBIOS Domain Name',
                3:'DNS Computer Name', 4:'DNS Domain Name',
                5:'DNS Tree Name', 7:'Timestamp', 9:'Target Name'}
    i = 0
    ti = b[ti_off:ti_off+ti_len]
    while i < len(ti):
        av_id, av_len = struct.unpack_from('<HH', ti, i)
        if av_id == 0: break
        val = ti[i+4:i+4+av_len]
        if av_id == 7:
            ts = struct.unpack('<Q', val[:8])[0]
            secs = (ts - 116444736000000000) / 10000000
            vs = datetime.fromtimestamp(secs, tz=timezone.utc).isoformat()
        else:
            vs = val.decode('utf-16-le', errors='ignore')
        print(f"  AV[{av_id}] {av_types.get(av_id, '?'):28s}: {vs!r}")
        i += 4 + av_len

Burp Collaborator NOT needed for this finding class — the data leak is in the synchronous response, not via OOB.

Common Root Causes

• Dual-auth IIS bindings on the public zone. Administrators leave NTLM enabled on the public-facing IIS site even when Forms auth is the intended entry point. Internal users get SSO; external attackers get the AD topology leak.

• Default IIS Application Pool identity left as ApplicationPoolIdentity. Combined with default hostname, signals provisioning never went past first-boot.

• Server never renamed from Windows-installer-generated hostname. Microsoft's default WIN-XXXXXXXXXXX 11-character pattern is the immediate tell. Sometimes also WORKGROUP\WIN-... in older boxes.

• Sub-domain joined to corporate forest without zone-isolation. European-integrator case: a a European importer's SharePoint test environment is a child domain inside a corporate global AD, disclosed via NTLM DNS Tree Name. The customer probably intends customer.parent-corp.example to be operationally separate but the NTLM Type-2 reveals the forest membership to anyone who probes.

• IIS Extended Protection NOT enabled. When <system.webServer><security><authentication><windowsAuthentication extendedProtection> is None (the default), the NTLM challenge is sent to any anonymous client. When set to Required, NTLM is restricted to authenticated callers — and the AV-pair leak is mitigated.

• No WindowsAuthentication removed from applicationHost.config for internet-exposed sites. SharePoint Central Admin sometimes leaves this enabled even when SP zone configuration only enables Forms.

Bypass Techniques

This skill describes a disclosure leak, not an authentication bypass. The "bypass" question is: *how do defenders block this AV-pair leak while still allowing legitimate NTLM auth?*

| Defense | Effectiveness |

|---|---|

| Disable NTLM on the public IIS binding entirely (Forms-only) | Best — eliminates the surface |

| IIS Extended Protection = Required | Restricts NTLM challenge to authenticated callers; AV-pair leak mitigated |

| Reverse-proxy strip WWW-Authenticate from anonymous responses | Sometimes works but breaks legitimate clients |

| Rate-limit the Type-1 → Type-2 endpoint | Doesn't prevent disclosure, only slows enumeration |

| Rename the Windows host from WIN-XXXXXXXXXXX | Removes the "lazy provisioning" tell; doesn't stop the leak |

| Move the SP/Exchange farm to a child AD with no cross-trust to corporate | Mitigates the *forest disclosure*; doesn't stop the leak |

For the attacker: there's no "bypass" needed — the leak is the finding.

Gate 0 Validation

Before writing the report, confirm:

• What can the attacker do RIGHT NOW with this disclosure?
• Internet-exposed + default hostname + corporate forest disclosed → Medium: attacker has UPN format for hunt-auth-bypass matrix probes, plus knows server has likely-default service accounts.
• Intranet-only or only NetBIOS name → Informational.

• Does the program accept information-disclosure findings without a chained impact?
• Many programs (Microsoft, large enterprise VDPs) DO accept this when the leaked info includes internal AD topology.
• Many programs (Shopify, GitHub) reject info disclosure without a chained impact.
• Read the program scope before submitting; if borderline, chain with a Tier-A finding from hunt-auth-bypass.

• Can you reproduce in <5 minutes from a fresh shell?
• The Python snippet above is the canonical reproduction. Include it verbatim in the report.

Real Impact Examples

Scenario A — Enterprise SharePoint inside parent corporate AD

Target: https://target-portal.example/ — a enterprise dealer portal (test mirror) operated by a system integrator.

Sending the anonymous Type-1 message to /_api/web/CurrentUser returned a Type-2 challenge whose AV_PAIRS decoded to:

NetBIOS Domain Name:    <CustomerName>
NetBIOS Computer Name:  WIN-XXXXXXXXXXX
DNS Domain Name:        customer.parent-corp.example
DNS Computer Name:      WIN-XXXXXXXXXXX.customer.parent-corp.example
DNS Tree Name:          customer.parent-corp.example
Timestamp:              2026-05-13T15:55:37.922Z

Three escalation paths:

• Default Windows-installer hostname (WIN-XXXXXXXXXXX) — server was never renamed after OS install; strong signal of lazy provisioning. Likely default service-account passwords on the SQL backend, default WSUS config, etc.
• Sub-domain inside corporate-parent AD (customer.parent-corp.example) — the customer is a child domain inside <ParentCorp>'s global Active Directory. A compromise of this test farm has potential cross-trust to corporate-parent.
• UPN format known — combined with hunt-auth-bypass's discovery of an anonymous brute-force endpoint on /_vti_bin/Authentication.asmx, the attacker has both the credential format ([email protected] or <CustomerName>\firstname.lastname) and the unlimited submission endpoint.

Reported severity: Medium, with a note that the chain with the Authentication.asmx anonymous brute-force makes the combined attack Critical.

Scenario B — Exchange edge with NTLM-protected EWS

Target: https://mail.example.com/EWS/Exchange.asmx. Type-1 probe returns Type-2 with DNS Tree Name corp.example.com and DNS Computer Name MAIL01.corp.example.com. Confirms the Exchange edge is domain-joined to corporate AD (rather than running in a DMZ-isolated AD). For an attacker with the matching hunt-mfa-bypass / hunt-auth-bypass chain, the leaked UPN format and server-name format accelerate credential spraying by removing the recon step. Reported severity: Low-Medium depending on program.

Scenario C — Intranet-only intentional leak (not a finding)

Target: https://intranet.corp.example (clearly internal, behind VPN). Type-1 returns full AV-pair set. Not reportable — this is intended NTLM behavior on intranet, and the disclosure is to authenticated VPN users who already see the same data via nltest /dsgetdc:corp.example.com. Recognize and drop.

Related Skills & Chains

• hunt-sharepoint — SharePoint farms emit anonymous Type-2 challenges on /_vti_bin/ by default; this is one of the most reliable ways to get internal AD topology. Chain primitive: SharePoint discovered → NTLM Type-2 capture on /_vti_bin/Lists.asmx → hunt-ntlm-info AV_PAIR decode → internal forest name → m365-entra-attack ROPC spray on Entra tenant tied to that forest.
• m365-entra-attack — Leaked NetBIOS domain + UPN suffix is the missing piece for a credible password spray. Chain primitive: NTLM Type-2 yields corp.example.com DNS tree → cross-reference Entra tenant via https://login.microsoftonline.com/corp.example.com/.well-known/openid-configuration → m365-entra-attack AADSTS error-differential username enumeration on resolved tenant.
• hunt-aspnet — IIS sites running ASP.NET frequently expose NTLM on management paths. Chain primitive: NTLM Type-2 on /owa/, /ecp/, /rpc/, /aspnet_client/ → confirm IIS + ASP.NET version → hunt-aspnet ViewState / .axd enumeration on same host.
• offensive-osint — The hostname pattern WIN-XXXXXXXXXXX signals lazy provisioning and predicts other weak hygiene. Chain primitive: NTLM Type-2 returns default-installer hostname → flag as low-maturity environment → offensive-osint deep recon (cert transparency, GitHub leakage, breach corpus correlation) is high-yield on this org.
• triage-validation — Most NTLM info-disclosure findings die at the 7-Question Gate on "is this exploitable" — pure topology disclosure is Low/Informational. Chain primitive: pull every NTLM-info finding through triage-validation BEFORE writing it up; only report if (a) leaks UPN format that accelerates spray, or (b) leaks production hostname mapping (redteam-report-template for the chain-narrative).