Category Archives: Nessus

Verify Permissions on files (Windows)

Objective

  • Changes to the permissions on files could block security settings from being applied.
  • Changes to the permissions on files could leak sensitive information.
  • Changes to the permissions on files could lead to a system compromise.
  • Audit files.

Manual audit with powershell

View the permission on the application log file with powershell

get-acl "C:\Windows\SYSTEM32\WINEVT\LOGS\application.evtx" | fl
Path : Microsoft.PowerShell.Core\FileSystem::C:\Windows\SYSTEM32\WINEVT\LOGS\application.evtx
Owner : NT AUTHORITY\LOCAL SERVICE
Group : NT AUTHORITY\LOCAL SERVICE
Access : NT SERVICE\EventLog Allow FullControl
NT AUTHORITY\SYSTEM Allow FullControl
BUILTIN\Administrators Allow FullControl
Audit :
Sddl : O:LSG:LSD:AI(A;ID;FA;;;S-1-5-80-880578595-1860270145-482643319-2788375705-1540778122)(A;ID;FA;;;SY)(A;ID;FA;;;
BA)

Audit with Nessus auditfile

<check_type: "Windows" version:"2">
<group_policy: "MS Windows Server">
 
<file_acl: "ACL_WINEVT_LOGS_application.evtx">
<user: "Administrators">
acl_inheritance: "inherited"
acl_apply: "this object only"
acl_allow: "full control"
</user>
 
<user: "System">
acl_inheritance: "inherited"
acl_apply: "this object only"
acl_allow: "full control"
</user>
 
<user: "EventLog">
acl_inheritance: "inherited"
acl_apply: "this object only"
acl_allow: "full control"
</user>
</acl>
 
<custom_item>
type: FILE_PERMISSIONS
description: "Audit file permissions om %SystemRoot%\SYSTEM32\WINEVT\LOGS\application.evtx"
value_type: FILE_ACL
value_data: "ACL_WINEVT_LOGS_application.evtx"
file: "C:\Windows\SYSTEM32\WINEVT\LOGS\application.evtx"
</custom_item>
 
</group_policy>
</check_type>

Error

Running this auditfile with this specific file results into an error because the file has a file lock.

Windows Compliance Checks, version 1.263
 
Which file contains your security policy : SMB login : stty: 'standard input': Inappropriate ioctl for device
SMB password : stty: 'standard input': Inappropriate ioctl for device
 
SMB domain (optional) : "Audit for %SystemRoot%\SYSTEM32\WINEVT\LOGS\application.evtx": [ERROR]
 
FILE_ERROR_FILE_CREATE: the file could not be opened. It could not be found or permissions were insufficient
 
file: C:\Windows\SYSTEM32\WINEVT\LOGS\application.evtx

Alternative approach

We can use the powershell command-let get-acl to perform the audit.
We run the command and filter out the known good values.

get-acl "C:\Windows\SYSTEM32\WINEVT\LOGS\setup.evtx" | select -ExpandProperty access | select IdentityReference,
FileSystemRights | Where {$_.IdentityReference -ne "NT SERVICE\EventLog" -and $_.IdentityReference -ne "NT AUTHORITY\S
YSTEM" -and $_.IdentityReference -ne "BUILTIN\Administrators" }

New Nessus Auditfile Check

<check_type: "Windows" version:"2">
<group_policy: "MS Windows Server">
 
<custom_item>
type : AUDIT_POWERSHELL
description : "Audit file permissions om %SystemRoot%\SYSTEM32\WINEVT\LOGS\application.evtx"
value_type : POLICY_TEXT
value_data : ""
powershell_args : 'get-acl \\"C:\\Windows\\SYSTEM32\\WINEVT\\LOGS\\setup.evtx\\" | select -ExpandProperty access | select IdentityReference, FileSystemRights | Where {$_.IdentityReference -ne \\"NT SERVICE\\EventLog\\" -and $_.IdentityReference -ne \\"NT AUTHORITY\\SYSTEM\\" -and $_.IdentityReference -ne \\"BUILTIN\\Administrators\\" }'
check_type : CHECK_EQUAL
powershell_option : CAN_BE_NULL
</custom_item>
 
</group_policy>
</check_type>

References

  • V-63533 – Permissions for the Application event log must prevent access by non-privileged accounts.
  • V-63537 – Permissions for the Security event log must prevent access by non-privileged accounts.
  • V-63541 – Permissions for the System event log must prevent access by non-privileged accounts

MS KB2871997: Update to Improve Credentials Protection and Management

Nessus Output:

Description
The remote host is missing one or more of the following Microsoft updates: KB2871997, KB2973351, KB2975625, KB2982378, KB2984972, KB2984976, KB2984981, KB2973501, or KB3126593. 
These updates are needed to improve the protection against possible credential theft.
- For Windows 7 / 2008 R2 :
KB2984972, KB2871997, KB2982378, and KB2973351 are required; also, KB2984976 (if KB2592687 is installed) or KB2984981 (if KB2830477 is installed).
- For Windows 8 / 2012 :
KB2973501, KB2871997, and KB2973351 are required.
- For Windows 8.1 / 2012 R2 :
KB2973351 (if Update 1 is installed) or KB2975625 (if Update 1 isn't installed).
These updates provide additional protection for the Local Security Authority (LSA), add a restricted administrative mode for Credential Security Support Provider (CredSSP), 
introduce support for the protected account-restricted domain user category, enforce stricter authentication policies, add additional protection for users' credentials, and add a restricted administrative mode for Remote Desktop Connection and Remote Desktop Protocol.
Solution
Microsoft has released a set of patches for Windows 7, 2008 R2, 8, 2012, 8.1, and 2012 R2.

Output
A required registry setting is missing:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\WDigest\UseLogonCredential = 0
More information: https://blogs.technet.microsoft.com/kfalde/2014/11/01/kb2871997-and-wdigest-part-1/

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SSL Version 2 and 3 Protocol Detection

Nessus Output:

Description

The remote service accepts connections encrypted using SSL 2.0 and/or SSL 3.0. These versions of SSL are affected by several cryptographic flaws. 
An attacker can exploit these flaws to conduct man-in-the-middle attacks or to decrypt communications between the affected service and clients.
NIST has determined that SSL 3.0 is no longer acceptable for secure communications. As of the date of enforcement found in PCI DSS v3.1, 
any version of SSL will not meet the PCI SSC'S definition of 'strong cryptography'.

Solution
Consult the application's documentation to disable SSL 2.0 and 3.0.
Use TLS 1.1 (with approved cipher suites) or higher instead.

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SSL DROWN Attack Vulnerability (Decrypting RSA with Obsolete and Weakened eNcryption)

Nessus Output:

Description

The remote host supports SSLv2 and therefore may be affected by a vulnerability that allows a cross-protocol Bleichenbacher padding oracle attack known as DROWN (Decrypting RSA with Obsolete and Weakened eNcryption). 
This vulnerability exists due to a flaw in the Secure Sockets Layer Version 2 (SSLv2) implementation, 
and it allows captured TLS traffic to be decrypted. 
A man-in-the-middle attacker can exploit this to decrypt the TLS connection by utilizing previously captured traffic and weak cryptography along with a series of specially crafted connections to an SSLv2 server that uses the same private key.

Solution

Disable SSLv2 and export grade cryptography cipher suites. 
Ensure that private keys are not used anywhere with server software that supports SSLv2 connections.

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SSL/TLS Diffie-Hellman Modulus <= 1024 Bits (Logjam)

Nessus Output:

Description
The remote host allows SSL/TLS connections with one or more Diffie-Hellman moduli less than or equal to 1024 bits. 
Through cryptanalysis, a third party may be able to find the shared secret in a short amount of time (depending on modulus size and attacker resources). 
This may allow an attacker to recover the plaintext or potentially violate the integrity of connections.

Solution
Reconfigure the service to use a unique Diffie-Hellman moduli of 2048 bits or greater.

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Server Message Block (SMB) Protocol Version 1 Unspecified RCE

Nessus Output

Description
The remote Windows host supports Server Message Block (SMB) Protocol version 1. 
It is, therefore, affected by an unspecified remote code execution vulnerability that allows an unauthenticated, 
remote attacker to execute arbitrary code.

Note that this vulnerability is one of multiple Equation Group vulnerabilities and 
exploits disclosed by a group known as the Shadow Brokers.

Solution
Disable SMBv1 according to the vendor instructions in Microsoft KB2696547. 
Additionally, block SMB directly by blocking TCP port 445 on all network boundary devices. 
For SMB over the NetBIOS API, block TCP ports 137 / 139 and UDP ports 137 / 138 on all network boundary devices.

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SSL Medium Strength Cipher Suites Supported

Nessus Output

Description

The remote host supports the use of SSL ciphers that offer medium strength encryption. 
Nessus regards medium strength as any encryption that uses key lengths at least 56 bits and less than 112 bits, or else that uses the 3DES encryption suite.

Note that it is considerably easier to circumvent medium strength encryption if the attacker is on the same physical network.

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Missing or Permissive Content-Security-Policy HTTP Response Header

Nessus Output

Synopsis :

The remote web server does not take steps to mitigate a class of web
application vulnerabilities.

Description :

The remote web server in some responses sets a permissive
Content-Security-Policy (CSP) response header or does not set one at
all.

The CSP header has been proposed by the W3C Web Application Security
Working Group as a way to mitigate cross-site scripting and
clickjacking attacks.

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DNS Server Cache Snooping Remote Information Disclosure

Nessus Output

Description
The remote DNS server responds to queries for third-party domains that do not have the recursion bit set.
This may allow a remote attacker to determine which domains have recently been resolved via this name server, and therefore which hosts have been recently visited.
For instance, if an attacker was interested in whether your company utilizes the online services of a particular financial institution, they would be able to use this attack to build a statistical model regarding company usage of that financial institution. Of course, the attack can also be used to find B2B partners, web-surfing patterns, external mail servers, and more.

Note: If this is an internal DNS server not accessible to outside networks, attacks would be limited to the internal network. This may include employees, consultants and potentially users on a guest network or WiFi connection if supported.

Solution
Contact the vendor of the DNS software for a fix.

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Link-Local Multicast Name Resolution (LLMNR) Detection

 Nessus Output

Synopsis :

The remote device supports LLMNR.

Description :

The remote device answered to a Link-local Multicast Name Resolution
(LLMNR) request. This protocol provides a name lookup service similar
to NetBIOS or DNS. It is enabled by default on modern Windows
versions.

Reported Risk factor by Nessus: None
In my option the severity should be much higher.

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MS KB3123479: Deprecation of SHA-1 Hashing Algorithm for Microsoft Root Certificate Program

Nessus Output

It appears KB3123479 has not been installed since the following
registry key does not exist and/or does not contain any of the following values :

HKEY_LOCAL_MACHINE\Software\Microsoft\Cryptography\OID\EncodingType 0\CertDllCreateCertificateChainEngine\Config\default

WeakSha1ThirdPartyFlags
WeakSha1ThirdPartyAfterTime

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