Malicious OAuth applications abuse cloud email services to spread spam

 Microsoft researchers recently investigated an attack where malicious OAuth applications were deployed on compromised cloud tenants and then used to control Exchange Online settings and spread spam. The investigation revealed that the threat actor launched credential stuffing attacks against high-risk accounts that didn’t have multi-factor authentication (MFA) enabled and leveraged the unsecured administrator accounts to gain initial access. The unauthorized access to the cloud tenant enabled the actor to create a malicious OAuth application that added a malicious inbound connector in the email server. The actor then used the malicious inbound connector to send spam emails that looked like they originated from the targets’ domain. The spam emails were sent as part of a deceptive sweepstakes scheme meant to trick recipients into signing up for recurring paid subscriptions.

Microsoft has been monitoring the rising popularity of OAuth application abuse. One of the first observed malicious usage of OAuth applications in the wild is consent phishing. Consent phishing attacks aim to trick users into granting permissions to malicious OAuth apps to gain access to user’s legitimate cloud services (mail servers, files storage, management APIs, etc.). In the past few years, Microsoft has observed that more and more threat actors, including nation-state actors, have been using OAuth applications for different malicious purposes – command-and-control (C2) communication, backdoors, phishing, redirections, and so on.

This recent attack involved a network of single-tenant applications installed in compromised organizations being used as the actor’s identity platform to perform the attack. As soon as the network was revealed, all the related applications were taken down and notifications to customers were sent, including recommended remediation steps.

This blog presents the technical analysis of this attack vector and the succeeding spam campaign attempted by the threat actor. It also provides guidance for defenders on protecting organizations from this threat, and how Microsoft security technologies detect it.

A diagram of the attack chain. It presents the flow of activity from left to right, starting with the attacker gaining access to its target tenant and leading to spam messages being sent to targets.
Figure 1. Overview of the attack chain. The time between application deployment and usage varied; there were cases where the actor took months before using the application.

Initial access

For the attack to succeed, the threat actor needed to compromise cloud tenant users with sufficient permissions that would allow the actor to create an application in the cloud environment and give it admin consent. The actor performed credential stuffing attacks against their targets, attempting to access users with the global admin role. The authentication attempts, which originated from a single IP address, were launched against the Azure Active Directory PowerShell application (app ID: 1b730954-1685-4b74-9bfd-dac224a7b894). The same application was later used to deploy the rest of the attack.

Based on the success ratio of the authentication attempts, it is inferred that the attacker used a dump of compromised credentials. The investigation also revealed that 86% of the compromised tenants had at least one admin with a real-time high risk score, which means they were flagged by Azure AD Identity Protection to be most likely compromised. It is also important to note that all the compromised admins didn’t have MFA enabled, which could have stopped the attack. These observations amplify the importance of securing accounts and monitoring for high-risk users, especially those with high privileges.

Deploying malicious OAuth application

Once the threat actor gained access to privileged users, their next step was to set up the malicious application. Based on analysis of the event user agent (Swagger-Codegen/1.4.0.0/csharp) and how quickly the deployment of the application was done, it is likely that the actor ran a PowerShell script to perform the following Azure Active Directory (AAD) management activities in all targeted tenants:

  • Register a new single–tenant application with the naming convention of [domain name]_([a-zA-Z]){3} (for example: Contoso_GhY)
  • Add the legacy permission Exchange.ManageAsApp which can be used for app-only authentication of Exchange Online PowerShell module
  • Grant admin consent to the above permission
  • Give global admin and Exchange Online admin roles to the previously registered application
  • Add application credentials (key/certificate/both)  

The threat actor added their own credentials to the OAuth application, which enabled them to access the application even if the initially compromised global administrator changed their password.

The activities mentioned gave the threat actor control of a highly privileged application. It was observed that the threat actor did not always use the application right after it was deployed. In some cases, it took weeks or months before the application was utilized. Also, in organizations that didn’t monitor for suspicious applications, the applications were deployed for months and used multiple times by the threat actor.


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CISA and NSA Publish Joint Cybersecurity Advisory on Control System Defense

 CISA and the National Security Agency (NSA) have published a joint
cybersecurity advisory about control system defense for operational technology
(OT) and industrial control systems (ICSs). Control System
Defense: Know the Opponent
is intended to provide critical infrastructure
owners and operators with an understanding of the tactics, techniques, and
procedures (TTPs) used by malicious cyber actors. This advisory builds on NSA
and CISA 2021 guidance provided to stop
malicious ICS activity against connect OT
, and 2020 guidance to reduce
OT exposure
.

CISA and NSA encourage critical infrastructure owners and operations to
review the advisory, [Control System Defense: Know the Opponent], and apply the
recommended mitigations and actions. For more information on CISA’s resources
and efforts to improve ICS cybersecurity, visit CISA’s role in industrial control systems webpage.

NIST IoT Cybersecurity Program Releases Two New Documents

 NIST’s Cybersecurity for the Internet of Things (IoT) program has
released two new documents:

The new consumer profile reflects the next steps discussed in the summary report on
the work done on the IoT cybersecurity labelling criteria portion of the work
responding to Executive Order
14028
. This profile builds on prior releases and the stakeholder
feedback they generated.

NIST Proposes the Conversion of FIPS 198-1 (HMAC) to a NIST Special Publication

 As a part of the periodic review of NIST’s cryptographic standards
and guidelines, NIST’s Crypto Publication Review Board
announced
the review of FIPS 198-1
The
Keyed-Hash Message Authentication Code (HMAC)
in August
2021. In response, NIST received
public comments.

NIST proposes to convert FIPS 198-1 to a NIST Special Publication
(SP), and apply the following changes:

  • Update the HMAC specification
    to include block sizes for the SHA-3 family of hash functions
  • Include a discussion on
    truncation
  • Improve the editorial quality
    and update references

Conversion to an SP: NIST typically specifies
fundamental cryptographic primitives—block ciphers, digital signatures
algorithms, and hash functions—as FIPS publications, whereas other
cryptographic schemes—modes of operation, message authentication codes,
etc.—are published as a part of the NIST SP 800 series. (For more information,
see Section 3 of NISTIR 7977.)
To be consistent with that approach, NIST proposes to convert FIPS 198-1 to an
SP.

In particular, NIST proposes to develop a draft SP for the HMAC
specification, updated as described above, which would be released for public
comment. When the SP is finalized and published, FIPS 198-1 would be withdrawn
simultaneously.

Send comments on the decision proposal by October 20, 2022 to cryptopubreviewboard@nist.gov
with “Comments on FIPS 198-1 decision proposal” in the subject
line.  


Comments received in response to this request will be posted on the Crypto
Publication Review Project site
after the due date. Submitters’
names and affiliations (when provided) will be included, while contact
information will be removed. See the project site for additional information
about the review process.

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Initial Public Draft of NIST IR 8427 Available for Comment

 The National Institute of Standards and Technology (NIST) has
released the initial public draft of NIST Interagency Report (IR) 8427,
Discussion on the Full Entropy Assumption of the SP 800-90
Series
. This document is being released at the same time as the
third public draft of NIST Special Publication (SP) 800-90C,
Recommendation for Random Bit Generator (RBG) Constructions,
in support of the SP 800-90 series of publications.

The NIST SP 800-90 series supports the generation of high-quality
random bits for cryptographic and non-cryptographic use. The security of a
random number generator depends on the unpredictability of its outputs, which
can be measured in terms of entropy. The NIST SP 800-90 series uses min-entropy
to measure entropy. A full-entropy bitstring has an amount of entropy equal to
its length. Full-entropy bitstrings are important for cryptographic
applications, as these bitstrings have ideal randomness properties and may be
used for any cryptographic purpose. Due to the difficulty of generating and
testing full-entropy bitstrings, the SP 800-90 series assumes that a bitstring
has full entropy if the amount of entropy per bit is at least 1 – ε, where ε is
at most 2-32. NIST IR 8427 provides a justification for the
selection of ε.

The public comment period for NIST IR 8427 is open through October
31, 2022.
See the publication
details
for a copy of the draft and instructions for submitting
comments.

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Request for Additional Digital Signature Schemes for the Post-Quantum Cryptography Standardization Process

The Post-Quantum Cryptography (PQC) standardization process is
continuing into a fourth round with the following key-encapsulation mechanisms
(KEMs) still under consideration: BIKE, Classic McEliece, HQC, and SIKE.
However, there are no remaining digital signature candidates under
consideration. As such,
NIST
is requesting additional digital signature proposals to be considered in the
PQC standardization process.

NIST is primarily interested in additional general-purpose
signature schemes that are not based on structured lattices. For certain
applications, such as certificate transparency, NIST may also be interested in
signature schemes that have short signatures and fast verification. NIST is
open to receiving additional submissions based on structured lattices but is
intent on diversifying the post-quantum signature standards.  As such, any
structured lattice-based signature proposal needs to significantly outperform
CRYSTALS-Dilithium and FALCON in relevant applications and ensure substantial
security properties in order to be considered for standardization.

Complete instructions on how to submit a candidate package,
including the minimal acceptability requirements, are posted on the PQC: Digital Signature Schemes project page.
The finalized evaluation criteria that will be used to assess the submissions
are also posted at the same website. Submission
packages must be received by NIST by June 1, 2023.

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Submit Comments on FIPS 180-4

 NIST is in the process of a periodic review and maintenance of its
cryptography standards and guidelines.   

This announcement initiates the review of Federal Information Processing
Standard (FIPS) 180-4
Secure Hash
Standard (SHS)
, 2015.

NIST requests public
comments on all aspects of FIPS 180-4
. Additionally, NIST would
appreciate feedback on the following two areas of particular concern:

  1. SHA-1. In recent years, the cryptanalytic attacks on the SHA-1
    hash function have become increasingly severe and practical (see, e.g., the 2020
    paper “SHA-1 is a Shambles” by Leurent and Peyrin
    ).
    NIST, therefore, plans to remove SHA-1 from a revision of FIPS 180-4 and
    to deprecate and eventually disallow all uses of SHA-1. The Cryptographic
    Module Validation Program
     will establish a validation
    transition schedule.

*  How will this
plan impact fielded and planned SHA-1 implementations?
*  What should NIST consider in establishing the timeline for disallowing
SHA-1?

  1. Interface. The “Init, Update, Final” interface was part
    of the SHA-3 Competition submission requirements. Should a revision of
    FIPS 180-4 discuss the “Init, Update, Final” hash function interface?

 The public comment period is open through September 9, 2022. Comments
may address the concerns raised in this announcement or other issues around
security, implementation, clarity, risk, or relevance to current
applications.  

Send comments to cryptopubreviewboard@nist.gov with
“Comments on FIPS 180-4” in the Subject. 

For more information about the review process, visit the Crypto
Publication Review Project page

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Microsoft has The Chief Information Security Officer (CISO) Workshop Training

 The Chief Information Security Office (CISO) workshop helps accelerate security program modernization with reference strategies built using Zero Trust principles.

The workshop covers all aspects of a comprehensive security program including strategic initiatives, roles and responsibilities, success metrics, maturity models, and more. Videos and slides can be found here.

This is free training

To learn more go here

Microsoft Exam Readiness Zone

This is a great resource for those pursuing Microsoft certification.

Join our experts as they provide tips, tricks, and strategies for preparing for a Microsoft Certification exam. Our exam prep videos will help you identify the key knowledge and skills measured on the exam and how to allocate your study time. Each video segment corresponds to a major topic area on the exam. Our trainer will point out objectives that many test takers find difficult. In these videos, we include example questions and answers with explanations. We recommend that you watch these videos after you have completed training or had some practice. However, you can watch them at any point in your certification journey. We also provide additional exam preparation resources

 

Exam Readiness Zone | Microsoft Docs