CVE-2021-42306 Vulnerability Analysis & Exploit Details

CVE-2021-42306 Vulnerability Summary

CVE-2021-42306: An information disclosure vulnerability manifests when a user or an application uploads unprotected private key data as part of an authentication certificate keyCredential  on an Azure AD Application or Service Principal (which is not recommended). This vulnerability allows a user or service in the tenant with application read access to read the private key data that was added to the application. Azure AD addressed this vulnerability by preventing disclosure of any private key values added to the application. Microsoft has identified services that could manifest this vulnerability, and steps that customers should take to be protected. Refer to the FAQ section for more information. For more details on this issue, please refer to the MSRC Blog Entry.

Exploit Prediction Scoring System (EPSS)

The EPSS score estimates the probability that this vulnerability will be exploited in the near future.

EPSS Score: 0.517% (probability of exploit)

EPSS Percentile: 77.03% (lower percentile = lower relative risk)
This vulnerability is less risky than approximately 22.97% of others.

CVE-2021-42306 References

External References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42306
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42306

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• Session Sidejacking CAPEC-102 Session sidejacking takes advantage of an unencrypted communication channel between a victim and target system. The attacker sniffs traffic on a network looking for session tokens in unencrypted traffic. Once a session token is captured, the attacker performs malicious actions by using the stolen token with the targeted application to impersonate the victim. This attack is a specific method of session hijacking, which is exploiting a valid session token to gain unauthorized access to a target system or information. Other methods to perform a session hijacking are session fixation, cross-site scripting, or compromising a user or server machine and stealing the session token.
• Signature Spoofing by Key Theft CAPEC-474 An attacker obtains an authoritative or reputable signer's private signature key by theft and then uses this key to forge signatures from the original signer to mislead a victim into performing actions that benefit the attacker.
• Password Recovery Exploitation CAPEC-50 An attacker may take advantage of the application feature to help users recover their forgotten passwords in order to gain access into the system with the same privileges as the original user. Generally password recovery schemes tend to be weak and insecure.
• Kerberoasting CAPEC-509 Through the exploitation of how service accounts leverage Kerberos authentication with Service Principal Names (SPNs), the adversary obtains and subsequently cracks the hashed credentials of a service account target to exploit its privileges. The Kerberos authentication protocol centers around a ticketing system which is used to request/grant access to services and to then access the requested services. As an authenticated user, the adversary may request Active Directory and obtain a service ticket with portions encrypted via RC4 with the private key of the authenticated account. By extracting the local ticket and saving it disk, the adversary can brute force the hashed value to reveal the target account credentials.
• Modify Existing Service CAPEC-551 When an operating system starts, it also starts programs called services or daemons. Modifying existing services may break existing services or may enable services that are disabled/not commonly used.
• Remote Services with Stolen Credentials CAPEC-555 This pattern of attack involves an adversary that uses stolen credentials to leverage remote services such as RDP, telnet, SSH, and VNC to log into a system. Once access is gained, any number of malicious activities could be performed.
• Use of Known Domain Credentials CAPEC-560 An adversary guesses or obtains (i.e. steals or purchases) legitimate credentials (e.g. userID/password) to achieve authentication and to perform authorized actions under the guise of an authenticated user or service.
• Windows Admin Shares with Stolen Credentials CAPEC-561 An adversary guesses or obtains (i.e. steals or purchases) legitimate Windows administrator credentials (e.g. userID/password) to access Windows Admin Shares on a local machine or within a Windows domain.
• Credential Stuffing CAPEC-600 An adversary tries known username/password combinations against different systems, applications, or services to gain additional authenticated access. Credential Stuffing attacks rely upon the fact that many users leverage the same username/password combination for multiple systems, applications, and services.
• Use of Captured Hashes (Pass The Hash) CAPEC-644 An adversary obtains (i.e. steals or purchases) legitimate Windows domain credential hash values to access systems within the domain that leverage the Lan Man (LM) and/or NT Lan Man (NTLM) authentication protocols.
• Use of Captured Tickets (Pass The Ticket) CAPEC-645 An adversary uses stolen Kerberos tickets to access systems/resources that leverage the Kerberos authentication protocol. The Kerberos authentication protocol centers around a ticketing system which is used to request/grant access to services and to then access the requested services. An adversary can obtain any one of these tickets (e.g. Service Ticket, Ticket Granting Ticket, Silver Ticket, or Golden Ticket) to authenticate to a system/resource without needing the account's credentials. Depending on the ticket obtained, the adversary may be able to access a particular resource or generate TGTs for any account within an Active Directory Domain.
• Use of Known Kerberos Credentials CAPEC-652 An adversary obtains (i.e. steals or purchases) legitimate Kerberos credentials (e.g. Kerberos service account userID/password or Kerberos Tickets) with the goal of achieving authenticated access to additional systems, applications, or services within the domain.
• Use of Known Operating System Credentials CAPEC-653 An adversary guesses or obtains (i.e. steals or purchases) legitimate operating system credentials (e.g. userID/password) to achieve authentication and to perform authorized actions on the system, under the guise of an authenticated user or service. This applies to any Operating System.

Vulnerable Configurations

• cpe:2.3:a:microsoft:azure_active_directory:-:*:*:*:*:*:*:*
  cpe:2.3:a:microsoft:azure_active_directory:-:*:*:*:*:*:*:*
• cpe:2.3:a:microsoft:azure_automation:-:*:*:*:*:*:*:*
  cpe:2.3:a:microsoft:azure_automation:-:*:*:*:*:*:*:*

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