jelasin/cve-2026-41089Pre-auth PoC for CVE-2026-41089 Netlogon CLDAP stack overflow via UDP/389, triggering LSASS crash/DC reboot. Includes exploit script, root-cause analysis, detection, and mitigation guidance.
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Windows Netlogon Remote Code Execution via CLDAP Stack Buffer Overflow
One crafted UDP packet to port 389 overflows a 528-byte stack buffer inside LSASS on any unpatched Windows Domain Controller. LSASS crashes. The DC reboots in about 60 seconds. No creds needed.
| Attack Vector | UDP 389 (CLDAP), pre-auth, zero credentials |
| Impact | LSASS crash, DC reboot, potential RCE |
| CWE | CWE-121 (Stack-based Buffer Overflow) |
| CVSS Vector | AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| Published | May 12, 2026 by Microsoft |
python3 poc.py 10.0.50.21 corp.local
The PoC sends a normal ping, then an overflow ping with a 130-char username, then checks if the DC survived. About 10 seconds total.
Windows Server versions acting as Domain Controllers:
| Server Version | Fixed In |
|---|---|
| 2012 / 2012 R2 | ESU-only patches |
| 2016 | 10.0.14393.9140 |
| 2019 | 10.0.17763.8755 |
| 2022 | 10.0.20348.5074 |
| 2022 23H2 | 10.0.25398.2330 |
| 2025 | 10.0.26100.32772 |
NlGetLocalPingResponse allocates a 528-byte stack buffer and hands
it to BuildSamLogonResponse. That function calls
NetpLogonPutUnicodeString to write server name, domain name, GUIDs,
and the attacker-controlled username into the buffer.
The bug: NetpLogonPutUnicodeString gets a max length in bytes but
reads it as a WCHAR count. Every string written through this path takes
up twice the expected space. The "User" field in the CLDAP filter (up
to 130 wchars, 260 bytes on the wire) pushes the combined write past
the 528-byte boundary.
I_NetLogonLdapLookupEx
-> NlGetLocalPingResponse // 528-byte stack buffer
-> LogonRequestHandler
-> BuildSamLogonResponse
-> NetpLogonPutUnicodeString // byte/WCHAR size confusion
python3 poc.py <target_ip> <domain_name> [options]
| Flag | Description | Default |
|---|---|---|
-l | Username length in characters | 130 |
-t | UDP recv timeout (seconds) | 5 |
-d | Delay between overflow and liveness check (seconds) | 3 |
# Connectivity test (short username, no overflow)
python3 poc.py 10.0.50.21 corp.local
# Default overflow attempt
python3 poc.py 10.0.50.21 corp.local -l 130
# Larger payload, longer timeout for slow networks
python3 poc.py 10.0.50.21 corp.local -l 200 -t 10
Python 3.8+. No third-party packages.
The overflow causes a DoS (LSASS crash, DC reboot). Stack corruption could enable RCE, but this PoC stays at DoS.
Network. Look for CLDAP search requests with a "User" filter attribute longer than 20-30 characters. Normal DC locator pings use short service account names.
Host. Watch for LSASS crashes tied to netlogon.dll (Event ID 1000). Turn on Netlogon debug logging:
nltest /dbflag:0x2080ffff
mov edx, 0x40 halves the max username length)Legal. This code exists for authorized security research and education. Test only against systems you own or have written permission to test. Unauthorized access to computer systems violates the CFAA and equivalent laws in most jurisdictions.