Microsoft Windows SMB NULL Session Authentication

high Nessus Plugin ID 26920
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It is possible to log into the remote Windows host with a NULL session.


The remote host is running Microsoft Windows. It is possible to log into it using a NULL session (i.e., with no login or password).

Depending on the configuration, it may be possible for an unauthenticated, remote attacker to leverage this issue to get information about the remote host.


Apply the following registry changes per the referenced Technet advisories :
Set :
- HKLM\SYSTEM\CurrentControlSet\Control\LSA\RestrictAnonymous=1
- HKLM\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters\restrictnullsessaccess=1

Reboot once the registry changes are complete.

See Also

Plugin Details

Severity: High

ID: 26920

File Name: smb_null_session.nasl

Version: 1.38

Type: remote

Agent: windows

Family: Windows

Published: 10/4/2007

Updated: 1/11/2022

Dependencies: smb_login.nasl

Risk Information

CVSS Score Source: CVE-2019-0519


Risk Factor: Medium

Score: 5.8


Risk Factor: High

Base Score: 7.5

Vector: AV:N/AC:L/Au:N/C:P/I:P/A:P


Risk Factor: High

Base Score: 7.3

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Vulnerability Information

CPE: cpe:/o:microsoft:windows

Required KB Items: SMB/null_session_suspected

Vulnerability Publication Date: 7/14/1999

Reference Information

CVE: CVE-1999-0519, CVE-1999-0520, CVE-2002-1117

BID: 494