Termsrv.dll Patch Windows Server 2019 Repack

Understanding the Termsrv.dll Patch for Windows Server 2019: Risks, Repacks, and Realities

1. License Violation (Most Severe)

Microsoft's EULA explicitly forbids modifying system binaries. Using this patch in a production environment exposes your organization to:

• Audit failure (Microsoft SAM audits).
• Legal liability.
• Invalidation of support contracts.

Step 4: Apply the Patch

Method A: Using a Patcher Tool (Recommended) This is where the "Repack" tools shine. Tools like the RDP Wrapper or specific "Universal Termsrv Patcher" executables automate the hex editing.

1. Download the patcher tool (ensure it is compatible with Server 2019 build numbers).
2. Run the tool as Administrator.
3. Click "Patch."
4. The tool will find termsrv.dll, modify the necessary bytes, and save the file.

Method B: Manual Hex Edit (For Advanced Users) If you are using a Hex editor (like HxD):

1. Open termsrv.dll in the Hex editor.
2. Search for the specific Hex string corresponding to your Server version. (These strings change between OS builds; you must find the correct offset for your specific termsrv.dll version).
3. Replace the string with the "unlocked" values (often changing a 74 byte to 75, or 0F to 90, depending on the jump instruction logic).
4. Save the file.

Procedure

1. Disable Real-Time Antivirus: Windows Defender often flags the patcher as "HackTool:Win32/Patcher." This is a false-positive based on behavior, but it will block execution. Termsrv.dll Patch Windows Server 2019 REPACK

2. Run the REPACK Tool as Administrator:

   • Most REPACKs include a patch.bat or Termsrv_patch.exe.
   • The script will typically stop the TermService (Remote Desktop Services) and UmRdpService (Remote Desktop Services UserMode Port Redirector).

3. Take Ownership & Bypass WFP:

   • The script uses takeown and icacls to grant the Administrator full control over termsrv.dll.
   • It may temporarily rename SFC.exe or disable the SFC scan via registry (HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SFCDisable).

4. Apply the Hex Patch:

   • The REPACK scans termsrv.dll for a unique hexadecimal signature.
   • For Server 2019, the common pattern is:
     • Original (limit 2 users): 8B 91 E4 00 00 00 83 FA 02 (or similar variations).
     • Patched (unlimited): Changes 83 FA 02 to 83 FA 00 (compare with 0 instead of 2) or replaces with 31 C0 90 90 90 (xor eax,eax / nop).
   • The REPACK automates this byte replacement.

5. Restart the Service (or Reboot):

   • The script restarts TermService.
   • Some REPACKs require a full reboot to load the patched DLL into memory.

6. Verify:

   • Open regedit and navigate to HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\Licensing Core.
   • If patched successfully, the value for EnableConcurrentSessions may be set to 1 (though this is not always necessary).
   • Attempt 3+ concurrent RDP connections from different user accounts.

---

The functions responsible for session limits:

• CConnectSessionManager::fVerifyClientLicense
• CConnectSessionManager::CheckServerLicense
• CSLSLicensing::IsLicensingEnabled

In an unpatched Windows Server 2019, these functions check: Understanding the Termsrv

• The number of active RDP sessions.
• Whether the server is in “Remote Desktop for Administration” mode (default 2 users).
• Presence of valid RDS CALs from a licensing server.

The patch modifies hex bytes within the DLL to:

• Change jump conditions (JNZ to JMP) so license checks always succeed.
• NOP (No Operation) out license enforcement routines.
• Hardcode the accepted session count to a high value (9999) or remove the check entirely.

What it is

• Termsrv.dll is the Windows Remote Desktop Services (RDS) server-side DLL that enforces licensing and session policies for Remote Desktop (RDP) on Windows Server.
• A "Termsrv.dll patch" or "repack" is an unofficial modification that alters Termsrv.dll to bypass Microsoft’s limitation that normally prevents multiple concurrent RDP sessions for non-RDS-licensed setups, or to re-enable concurrent interactive logons for administrative accounts.
• "Repack" typically refers to a packaged distribution of the patched DLL (or files and an installer script) that replaces the original system file with a modified version.

---

The Evolution: Why a "REPACK" for Server 2019?

The original Termsrv.dll patch has existed since the Windows 2000/XP days. However, Windows Server 2019 (build 1809 and later) introduced significant security mitigations:

1. PatchGuard (Kernel Patch Protection): While Termsrv.dll is user-mode, Microsoft hardened binary integrity checks.
2. Windows File Protection (WFP) / System File Checker (SFC): Replaces modified system files automatically.
3. Digital Signatures: Modern Windows checks for valid Authenticode signatures on critical system DLLs. A modified Termsrv.dll breaks the signature.

Older patching tools (e.g., Universal Termsrv.dll Patch v2.x) often failed on Server 2019, leading to blue screens, boot loops, or simply being reverted by SFC. Audit failure (Microsoft SAM audits)

The "REPACK" label indicates that a community group or cracker has:

• Reversed Microsoft's newer checks.
• Updated the byte patterns for Server 2019 RTM and later cumulative updates.
• Repackaged the tool with automated scripts (e.g., batch files to stop RDP services, take ownership, disable SFC temporarily).
• Often bundled with a pre-modified Termsrv.dll file for specific build numbers (e.g., 17763, 20348).

---

5. Developer/Test Workarounds

For non-production labs:

• Use Hyper-V to create multiple small VMs instead of one big server.
• Use eval versions (180-day trial) that allow unlimited RDP sessions legally.
• Reset the trial using slmgr /rearm (not advised for production).

---