Add content from: Bypassing Windows authentication reflection mitigations for ...

Author: HackTricks News Bot

src/SUMMARY.md

@@ -287,6 +287,7 @@
   - [Integrity Levels](windows-hardening/windows-local-privilege-escalation/integrity-levels.md)
   - [JuicyPotato](windows-hardening/windows-local-privilege-escalation/juicypotato.md)
   - [Leaked Handle Exploitation](windows-hardening/windows-local-privilege-escalation/leaked-handle-exploitation.md)
+  - [Local NTLM Reflection via SMB Arbitrary Port](windows-hardening/windows-local-privilege-escalation/local-ntlm-reflection-via-smb-arbitrary-port.md)
   - [MSI Wrapper](windows-hardening/windows-local-privilege-escalation/msi-wrapper.md)
   - [Named Pipe Client Impersonation](windows-hardening/windows-local-privilege-escalation/named-pipe-client-impersonation.md)
   - [Privilege Escalation with Autoruns](windows-hardening/windows-local-privilege-escalation/privilege-escalation-with-autorun-binaries.md)

src/windows-hardening/ntlm/README.md

@@ -342,6 +342,12 @@ krbrelayx.py -t TARGET.DOMAIN.LOCAL -smb2support
 * Kerberos AP-REQ containing a subsession key and a client principal equal to the hostname.
 * Windows Event 4624/4648 SYSTEM logons immediately followed by remote SMB writes from the same host.
 
+For the **March 2026** local reflection variant that abuses **SMB arbitrary ports** and **TCP connection reuse** to reach `NT AUTHORITY\SYSTEM`, see:
+
+{{#ref}}
+../windows-local-privilege-escalation/local-ntlm-reflection-via-smb-arbitrary-port.md
+{{#endref}}
+
 ## References
 * [NTLM Reflection is Dead, Long Live NTLM Reflection!](https://www.synacktiv.com/en/publications/la-reflexion-ntlm-est-morte-vive-la-reflexion-ntlm-analyse-approfondie-de-la-cve-2025.html)
 * [MSRC – CVE-2025-33073](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-33073)

src/windows-hardening/windows-local-privilege-escalation/README.md

@@ -56,6 +56,12 @@ Secure Desktop accessibility registry propagation can be abused for an arbitrary
 secure-desktop-accessibility-registry-propagation-regpwn.md
 {{#endref}}
 
+Recent Windows builds also introduced an **SMB arbitrary-port** LPE path where a privileged local NTLM authentication is reflected over a reused SMB TCP connection:
+
+{{#ref}}
+local-ntlm-reflection-via-smb-arbitrary-port.md
+{{#endref}}
+
 ## System Info
 
 ### Version info enumeration

src/windows-hardening/windows-local-privilege-escalation/local-ntlm-reflection-via-smb-arbitrary-port.md

@@ -0,0 +1,110 @@
+# Local NTLM Reflection via SMB Arbitrary Port
+
+{{#include ../../banners/hacktricks-training.md}}
+
+Recent Windows builds introduced **SMB client support for alternative TCP ports**. That feature can be abused to turn **local NTLM authentication** into a **SYSTEM local privilege escalation** when the attacker can:
+
+1. Open an SMB connection to an attacker-controlled listener on a **non-445 port**
+2. Keep that TCP connection alive
+3. Coerce a **privileged local client** to access the **same SMB share path**
+4. Relay the resulting **local NTLM authentication** back to the machine's real SMB service
+
+This is the primitive behind **CVE-2026-24294**, patched in **March 2026**.
+
+## Why it works
+
+The older CMTI / serialized-SPN reflection trick is covered here:
+
+{{#ref}}
+../ntlm/README.md
+{{#endref}}
+
+This newer variant does **not** need a marshalled hostname. Instead it abuses two SMB client behaviours:
+
+- **Alternative port support** on **Windows 11 24H2** and **Windows Server 2025**, exposed to users with `net use \\host\share /tcpport:<port>`
+- **SMB connection reuse / multiplexing**, where multiple authenticated sessions can ride the same TCP connection
+
+That means a low-privileged user can first create a TCP connection from the SMB client to an attacker SMB server on a high port, then coerce a privileged service to access the **exact same UNC path**. If Windows decides to reuse the existing TCP connection, the privileged NTLM exchange is sent over the attacker-controlled transport and can be relayed to the local SMB server.
+
+## Preconditions
+
+- Target supports SMB alternative ports:
+  - **Windows 11 24H2** or later
+  - **Windows Server 2025** or later
+- The attacker can run a local or remote SMB server on a chosen high port
+- The attacker can coerce a privileged service to access a UNC path
+- The privileged authentication must be **NTLM local authentication**
+- The target must be relayable:
+  - Synacktiv reported it worked by default on **Windows Server 2025**
+  - Their chain did **not** work on **Windows 11 24H2** because outbound SMB signing is enforced there by default
+
+## Userland and internals
+
+From the command line the feature looks simple:
+
+```cmd
+net use \\192.168.56.3\share /tcpport:12345
+```
+
+Programmatically, the client uses `WNetAddConnection4W` with undocumented `lpUseOptions` data. The relevant option is `TraP` (transport parameters), which eventually reaches the kernel SMB client through an FSCTL and is parsed by `mrxsmb`.
+
+Important practical notes:
+
+- **UNC syntax still has no port field**
+- **`net use` is per-logon-session**
+- The bypass still works because **the TCP connection and the SMB session are separate objects**
+- Reusing the **same share path** is mandatory if the exploit depends on the SMB client reusing the previously created TCP connection
+
+## Exploitation flow
+
+### 1. Create the attacker-controlled SMB transport
+
+Run an SMB server on a high port and make Windows connect to it:
+
+```cmd
+net use \\192.168.56.3\share /tcpport:12345
+```
+
+The server can accept any credential pair you control, for example `user:user`. The goal of this step is not privilege escalation yet, only to make the Windows SMB client open and keep a reusable TCP connection to your listener.
+
+### 2. Coerce a privileged service to the same UNC path
+
+Use a coercion primitive such as **PetitPotam** against the **same** `\\192.168.56.3\share` path. If the coerced client is privileged and the target name is local (`localhost` or a local IP/host), Windows performs **NTLM local authentication**.
+
+Because the TCP connection is reused, that privileged NTLM exchange travels to the attacker SMB service instead of directly to the real local SMB server.
+
+### 3. Relay the privileged authentication back to local SMB
+
+The attacker-controlled SMB service forwards the privileged NTLM exchange to `ntlmrelayx.py`, which relays it to the machine's real SMB listener and obtains a session as `NT AUTHORITY\SYSTEM`.
+
+Typical tooling from the public writeup:
+
+- `smbserver.py` on a custom port to receive the privileged auth over the reused TCP connection
+- `ntlmrelayx.py` to relay the captured NTLM to local SMB
+- `PetitPotam.exe` or another coercion primitive to force the privileged authentication
+
+## Operator notes
+
+- This is a **local privilege escalation** technique, not a generic remote relay trick
+- The attacker-controlled SMB service must handle the privileged authentication on the **same TCP connection** originally used for the share mount
+- If the coerced access hits a **different share path**, Windows may establish a different connection and the chain breaks
+- SMB signing requirements can kill the relay even when the arbitrary-port step works
+- If you only have Kerberos material or cannot force local NTLM, this exact variant is not enough
+
+## Detection and hardening
+
+- Patch **CVE-2026-24294** from **March 2026 Patch Tuesday**
+- Watch for `net use` or `New-SmbMapping` using **non-default SMB ports**
+- Alert on unusual outbound SMB from workstations or servers to **high TCP ports**
+- Review coercion opportunities such as **EFSRPC / PetitPotam-style** triggers
+- Enforce SMB signing where possible; Synacktiv specifically notes this blocked their relay on Windows 11 24H2
+
+## References
+
+- [Synacktiv - Bypassing Windows authentication reflection mitigations for SYSTEM shells - Part 1](https://www.synacktiv.com/en/publications/bypassing-windows-authentication-reflection-mitigations-for-system-shells-part-1.html)
+- [Microsoft Learn - Configure alternative SMB ports for Windows Server 2025](https://learn.microsoft.com/en-us/windows-server/storage/file-server/smb-ports)
+- [Microsoft Learn - WNetAddConnection4W](https://learn.microsoft.com/en-us/windows/win32/api/winnetwk/nf-winnetwk-wnetaddconnection4w)
+- [Project Zero - Windows Exploitation Tricks: Trapping Virtual Memory Access (2025 Update)](https://projectzero.google/2025/01/windows-exploitation-tricks-trapping.html)
+- [MSRC - CVE-2026-24294](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-24294)
+
+{{#include ../../banners/hacktricks-training.md}}