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New Vulnerabilities Bypass Multi-Factor Authentication for Microsoft 365

Proofpoint researchers recently discovered critical vulnerabilities in multi-factor authentication (MFA) implementation in cloud environments where WS-Trust is enabled. These vulnerabilities could allow attackers to bypass MFA and access cloud applications that use the protocol, notably Microsoft 365. Due to the way Microsoft 365 session login is designed, an attacker could gain full access to the target’s account (including mail, files, contacts, data and more). Furthermore, these vulnerabilities could also be used to gain access to various other Microsoft-provided cloud services, including production and development environments such as Azure and Visual Studio.

The vulnerabilities were announced by Proofpoint and demonstrated at our virtual user conference, Proofpoint Protect. Most likely, these vulnerabilities have existed for years. We have tested several Identity Provider (IDP) solutions, identified those that were susceptible and resolved the security issues.

The vulnerabilities were a result of the “inherently insecure protocol” (WS-Trust) as described by Microsoft combined with various bugs in its implementation by the IDPs. In some cases, an attacker could spoof his IP address to bypass MFA via a simple request header manipulation. In another case, altering the user-agent header caused the IDP to misidentify the protocol and believe it to be using Modern Authentication. In all cases, Microsoft logs the connection as “Modern Authentication” due to the exploit pivoting from legacy protocol to the modern one. Unaware of the situation and the risks involved, the administrators and security professionals monitoring the tenant would see the connection as made via Modern Authentication.

Vulnerabilities require research, but once discovered, they can be exploited in an automated fashion.  They are hard to detect and may not even appear on event logs, leaving no trace or hint of their activity. Since MFA as a preventative measure can be bypassed, it becomes necessary to layer additional security measures in the form of account compromise detection and remediation.

MFA Adoption Accelerates During the Pandemic

Multi-factor authentication (MFA) is quickly becoming a must-have security layer for cloud applications. During the global pandemic, the demand for cloud-based applications such as messaging and collaboration platforms surged as organizations shifted to work from home. Employees started accessing corporate applications from personal and unmanaged devices. And they started spending more time on their corporate devices at home, reading potentially malicious personal emails, or browsing risky websites.

COVID-19-themed attacks successfully took advantage of people’s concerns to compromise their credentials, increasing the security risk of unauthorized access to corporate cloud applications.  MFA can help reduce your organization’s attack surface by adding another layer of account security. It supplements the username and password model with another factor that only the user possesses such as their mobile phone. Yet, as the new vulnerabilities show, MFA does not provide enough security on its own.

How Attackers Bypass MFA

Some commonly known MFA-bypass methods are real-time phishing, channel hijacking and the use of legacy protocols.

Real-time phishing

Unlike regular phishing, real-time phishing involves stealing the user’s extra factor. In some cases, the attacker may create a “proxy” between the target website and the victim. The “proxy” looks similar to the original website. Using this imposter website, the attacker manipulates the victim to hand over the authentication code along with his credentials. Such attacks can be automated using tools like Modlishka. However, the attackers must update their tools frequently in order to avoid detections from large vendors and need more complex infrastructure.

Another real-time phishing method attackers use is “challenge reflection,” where the users are prompted to fill MFA credentials at a phishing site, and they are distributed to the attackers in real-time. While this method does not require a man-in-the-middle, it usually involves a real person facilitating the entire process of account compromise for each targeted account.

Channel hijacking

Channel hijacking attacks the victim’s phone or computer, usually with malware. PC malware can use man-in-the-browser or web injects to get information. Some malware steals the MFA from the phone. In some cases, attackers even steal text messages via the cell tower directly or via a rouge cell tower, taking over the victim phone number or hacking to their voice answering machine.

Legacy protocols

A cheaper and more scalable method of bypassing MFA leverages legacy protocols for attacks on cloud accounts. Many organizations continue to allow legacy protocols to be able to support legacy devices or applications such as copy machines or shared accounts such as conference rooms. Legacy email protocols like POP and IMAP do not support MFA with non-interactive applications so they cannot enforce it. This bypass method is easily automated and applied to credential dumps from the web or credentials obtained from phishing. Even though organizations started to block legacy protocols or allow them only for some specific users, the problem persists. 

Proofpoint cloud threats research showed that in the first half of 2020, 97% of organizations came under brute force attacks and 30% of them had at least one compromised cloud account. When we studied email-based cloud attacks (credential phishing, malware, etc.) we found that 73% of all monitored tenants are targeted and 57% are compromised. When it comes to cloud security, MFA is not a silver bullet. As more organizations adopt the technology, more vulnerabilities will be discovered and abused by attackers. However, MFA can improve overall security posture, especially when combined with people-centric threat visibility and adaptive access controls.

Combine MFA and Threat Visibility to Secure Cloud Applications

As a first layer of SaaS and IaaS protection, Proofpoint CASB provides adaptive access controls to help you prevent account take-over. These real-time security measures are based on risk, context, role and Proofpoint’s Very Attacked People profiling. Here’s what we empower you to do:

  • Automatically block access from risky locations and networks and by known threat actors.
  • Apply people-centric policies to high-risk and high-privilege users.
  • Enforce more granular controls: MFA, access via browser isolation, log in via VPN, etc.

Unlike static security and compliance controls that apply to every user in the same way, CASB-enabled access controls are adaptive. They allow you to apply just the right amount of security and compliance controls without unduly burdening lower-risk users.

Given the risk of MFA bypass, CASB provides people-centric threat visibility as a second layer of protection.  Proofpoint combines cross-channel (cloud, email and more) threat intelligence with user-specific contextual data from application logs to analyze user behavior and detect anomalies across cloud apps and tenants. Through machine learning and rich threat intelligence, we help you detect, investigate and automatically remediate cloud account takeover.

Learn More:

Learn more about Proofpoint’s solution by downloading our whitepaper, Getting Started with CASB. To view the session on Bypassing MFA for Cloud Applications and the demo of the vulnerabilities, register for Proofpoint Protect here.

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