Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Security Management //

Authentication

6/13/2019
04:38 PM
Larry Loeb
Larry Loeb
Larry Loeb
50%
50%

Preempt Shows How to Sidestep EPA Authentication

Security firm Preempt issued an advisory that showed how to conceptually bypass the Enhanced Protection for Authentication that prevents attackers from performing a relay of NT Lan Manager messages to top-level security sessions.

Security firm Preempt issued an advisory that showed how to conceptually bypass the Enhanced Protection for Authentication (EPA) that prevents attackers from performing a relay of NT Lan Manager (NTLM) messages to top-level security (TLS) sessions. Attackers could use NTLM to enable their own fake sessions. Since a relay attack is the most common one used against the proprietary NTLM, EPA was put there to stop them.

Preempt says that their "bypass allows attackers to modify NTLM messages to generate legitimate channel binding information. This can allow attackers to connect to various web servers using the attacked user's privileges and perform operations such as: read the user's emails (by relaying to Outlook Web Access (OWA) servers) or even connect to cloud resources (by relaying to Active Directory Federation Services (ADFS) servers)."

Also, the Message Integrity Code (MIC) is not tampered with. Instead, it is just cut out. The advisory says, "bypass allows attackers to remove the 'MIC' protection and modify various fields in the NTLM authentication flow, such as signing negotiation."

But wait, one more.

Server Message Block (SMB) Session Signing was to prevent attackers from relaying NTLM authentication messages to establish SMB and other sessions. It's the same relay attack, but the defense tool was adapted for this specific situation.

The researchers went on, "The bypass we discovered enables attackers to relay NTLM authentication requests to any server in the domain, including domain controllers, while establishing a signed session to perform remote code execution. If the relayed authentication is of a privileged user, this means full domain compromise."

Boy Howdy, that's a #fail.

They patched the bypass in the June Patch Tuesday. But just the patching alone is not sufficient to deal with this and other problems.

Preempt says that configuration changes should be done to the network. Because it's NTLM, you know?

Some really relevant network options are:

 

  • Enforce SMB Signing -- To prevent attackers from launching simpler NTLM relay attacks, turn "SMB Signing" on throughout the network.

 

 

  • Block NTLMv1 -- Since NTLMv1 is considered significantly less secure, it is recommended to completely block it by setting the appropriate GPO. Why make it worse than it has to be?

 

 

  • Enforce LDAP/S Signing -- To prevent NTLM relay in Lightweight Directory Access Protocol (LDAP), enforce LDAP signing and LDAPS channel binding on domain controllers.

 

 

  • Enforce EPA -- To prevent NTLM relay on web servers, harden all web servers (OWA, ADFS) to accept only requests with EPA. Reduce NTLM usage - Even with a fully secure configuration and fully patched servers NTLM still poses a significantly greater risk to most analysts than Kerberos. Preempt recommends that you remove NTLM anywhere it is not needed.

 

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
Why Vulnerable Code Is Shipped Knowingly
Chris Eng, Chief Research Officer, Veracode,  11/30/2020
Register for Dark Reading Newsletters
White Papers
Video
Cartoon Contest
Write a Caption, Win an Amazon Gift Card! Click Here
Latest Comment: I think the boss is bing watching '70s TV shows again!
Current Issue
2021 Top Enterprise IT Trends
We've identified the key trends that are poised to impact the IT landscape in 2021. Find out why they're important and how they will affect you today!
Flash Poll
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2020-26246
PUBLISHED: 2020-12-03
Pimcore is an open source digital experience platform. In Pimcore before version 6.8.5 it is possible to modify & create website settings without having the appropriate permissions.
CVE-2020-29279
PUBLISHED: 2020-12-02
PHP remote file inclusion in the assign_resume_tpl method in Application/Common/Controller/BaseController.class.php in 74CMS before 6.0.48 allows remote code execution.
CVE-2020-29280
PUBLISHED: 2020-12-02
The Victor CMS v1.0 application is vulnerable to SQL injection via the 'search' parameter on the search.php page.
CVE-2020-29282
PUBLISHED: 2020-12-02
SQL injection vulnerability in BloodX 1.0 allows attackers to bypass authentication.
CVE-2020-29283
PUBLISHED: 2020-12-02
An SQL injection vulnerability was discovered in Online Doctor Appointment Booking System PHP and Mysql via the q parameter to getuser.php.