Mitigating Service Account Credential Theft on Windows

Summary:

The document outlines several strategies for mitigating the risk of service account credential theft on Windows systems, focusing primarily on Kerberos and NTLM authentication protocols. To reduce vulnerabilities associated with automated authentication against untrusted endpoints, recommendations include: 1. **Upgrading Encryption Types**: Advise using stronger encryption types such as AES128-CTS-HMAC-SHA1-96 and AES256-CTS-HMAC-SHA1-96 instead of weaker ones like DES-CBC-CRC or DES-CBC-MD5 to protect against brute force attacks. 2. **Implementing Strong Password Policies**: Encourage the use of complex passwords that cannot be easily cracked, particularly for service accounts which should not have interactive logons enabled. 3. **Utilizing Free and Open-Source Security Tools**: Recommend tools like KerbCrack, Cain & Abel, and ElcomSoft Password Recovery to test system vulnerabilities and identify weaknesses in password protection mechanisms. 4. **Monitoring Network Traffic for Anomalies**: Implement network monitoring systems that can detect unusual patterns of traffic or failed authentication attempts which might indicate an attack on service accounts. 5. **Regular Audits and Security Posture Reviews**: Routinely review the security configurations of systems to ensure they comply with best practices, especially concerning password management and encryption settings for Kerberos and NTLM. 6. **Updating Systems to Newer Versions**: Encourage upgrading to newer versions of Windows that include patches against known vulnerabilities in older system components which could be exploited by attackers looking to steal credentials. 7. **Blocking Legacy Protocols**: Where possible, restrict the use of SMB1 and other legacy protocols due to their susceptibility to various forms of attacks related to credential theft. 8. **Implementing Multi-Factor Authentication (MFA)**: Encourage adoption of MFA for all accounts, including service accounts, which adds an additional layer of security beyond just passwords. 9. **Maintaining Up-to-Date Security Software and Patches**: Ensure that antivirus software, firewalls, and other security tools are updated with the latest definitions and patches to protect against new threats. 10. **Educating Users About Phishing Attacks**: Train employees on how to recognize and avoid phishing scams designed to trick them into revealing their credentials or compromising system passwords. These recommendations should be considered in conjunction with other security measures such as network segmentation, least privilege access policies, and regular security audits. It is important for organizations to evaluate the specific risks they face and tailor these mitigation strategies accordingly.

Details:

This document provides a guide on mitigating service account credential theft on Windows systems, focusing on reducing risks associated with automated authentication against untrusted endpoints. It addresses various attack vectors including Kerberos and NTLM vulnerabilities, strategies for defending against these attacks, and recommendations to harden the system. The authors emphasize that while they cannot guarantee the protection of any particular system from all potential threats, their goal is to provide guidance on how to reduce risk through proper configuration and monitoring. This document discusses the vulnerabilities in automated authentication processes on Windows systems, particularly those used by privileged services. It highlights how attackers can exploit these weaknesses to steal credentials through various methods like NTLM and Kerberos protocols. The paper provides practical mitigation strategies for common versions of Windows operating system to prevent such attacks, focusing on managing service accounts and their configuration. This text discusses the vulnerabilities associated with Kerberos and NTLM authentication protocols in Windows environments, particularly concerning the theft of service account credentials. It highlights that an attacker can exploit these weaknesses to gain unauthorized access by intercepting communication between a Kerberos client and KDC or through MITM attacks on NTLM sessions. The text explains how using weaker encryption types like DES-CBC-CRC or DES-CBC-MD5 in passwords can lead to their recovery via brute force attacks. It recommends upgrading to stronger password policies, such as those that use AES128-CTS-HMAC-SHA1-96 and AES256-CTS-HMAC-SHA1-96 encryption types, which are supported by Windows Vista and Server 2008 but not by legacy systems like Windows XP or Server 2003. It also discusses NTLMv1 challenge-response authentication protocol weaknesses, where an attacker can perform offline brute force attacks to recover the user’s password hashes even if the actual plaintext password is unknown. This makes it crucial for users to employ strong passwords that cannot be easily cracked. The text concludes by recommending the use of free and open-source security tools like KerbCrack, Cain & Abel, and ElcomSoft Password Recovery for demonstrating these issues and suggests migrating from unsupported legacy systems to newer versions such as Windows 8.1 and Server 2012 R2 for enhanced security features and support. The text discusses various methods for cracking passwords, particularly in the context of NTLMv2 challenge-response authentication used in Windows systems. It explains how certain types of attacks can be mitigated or detected based on system settings and protocols like SMB (Server Message Block) and NTLM (NT LAN Manager). Key points include: 1. **Cracking DES Keys**: An offline brute-force attack can be effective against legacy Triple-DES (3DES) encryption keys used in certain authentication mechanisms, particularly when dealing with 7-byte blocks within a 16-byte input. The focus of such attacks is usually on the first two out of three DES keys, as the third key can often be calculated quickly due to its limited length. 2. **NTLMv2 vs. NTLMv1**: Unlike older NTLMv1, which uses DES encryption for the nonce, NTLMv2 employs an MD5-based HMAC (Hash-based Message Authentication Code) using the user's NTOWF key as the cryptographic key. This makes it more resistant to offline brute-force attacks because current computational power cannot feasibly crack all possible keys in the case of MD5 HMAC. However, NTLMv2 is still vulnerable to attacks where an attacker can act as an oracle and perform a brute-force attack on the password itself if it's weak enough. 3. **Downgrade Attacks**: These are effective against systems with default settings in Windows Vista and Server 2008 but remain feasible for older versions like Windows XP and Server 2003, especially when network policies allow NTLMv1 compatibility. The attacker can intercept the authentication process between a client and server to force it to use an outdated version of NTLM. 4. **NTLM Relay Attacks**: These attacks exploit vulnerabilities in NTLMv1 and NTLMv2 where an attacker can relay connections, gaining access to authenticated sessions on target servers even if they are not directly MITMed due to network configurations or policies that support legacy authentication methods. 5. **Tools for Exploitation**: Various open-source and free tools like Responder, Squirtle, Cain & Abel, SMBRelay3, and the Metasploit Framework exist to demonstrate these vulnerabilities and facilitate attacks. Tools are also available for offline brute-force using software such as John the Ripper, L0phtcrack, HashCat, oclHashCat, and others. 6. **Mitigation Strategies**: Over time, Microsoft has enhanced authentication protocols with improvements like SHA256 message signing in SMB v2 and AES-based encryption in SMB v3, but legacy systems often remain a challenge due to compatibility issues. Organizations can implement mitigations such as disabling unnecessary protocol versions or using stronger password policies to reduce the risk of attacks. In summary, while technological advancements have introduced more secure authentication methods over time, many organizations still rely on older systems and configurations that make them susceptible to various types of attacks detailed in this text. The effectiveness of mitigating these risks depends largely on understanding and implementing appropriate security controls based on system capabilities and organizational policies. The document outlines strategies for improving security against service account credential theft on Windows systems, focusing on Kerberos and NTLM authentication protocols. Recommendations include disabling weaker HMAC algorithms in Kerberos (encouraging AES-256), enabling Kerberos Armoring to protect against brute force attacks, and enforcing strict password policies for service accounts. For NTLM, it suggests transitioning to Kerberos where possible, disabling NTLM on clients and servers, mandating the use of SMB signing, and phasing out older SMB versions like SMB1. The document emphasizes that these recommendations are not exhaustive but provide practical steps for organizations to enhance their security posture against determined adversaries with administrative access. The article discusses the management and security of service accounts, particularly in the context of Windows servers and Active Directory environments. It provides guidelines for reducing the privileges of service accounts, automating password changes using PowerShell or third-party tools, and utilizing Group Managed Service Accounts (gMSA) on Server 2012 domain controllers for automatic password rolling. The article also addresses the use of LDAP services in mitigating credential theft by enforcing security measures such as SASL/Sicily for service bindings, mandating signing of all LDAP requests to prevent replay attacks, and monitoring bind attempts with STARTTLS. Additionally, it stresses the importance of hardening the network perimeter through firewall rules that block unnecessary outbound access on ports 88, 135, 139, and 445 for TCP and UDP ports 137, 138, and 88, to prevent credential harvesting via UNC paths. The article recommends enhancing monitoring by collecting events from various devices and storing them in a system that supports full-text searches, with options including commercial SIEM products, open-source tools like Eventlog to Syslog Service, and Microsoft's own Sysmon service for generating detailed event logs. Finally, the article warns against using simple authentication methods which could be exploited by credential theft attempts. Overall, it provides a comprehensive set of recommendations aimed at protecting Windows servers from unauthorized access due to compromised service accounts. The passage highlights several aspects related to mitigating the theft of service account credentials, particularly when interactive logins are disabled for such accounts. It suggests that various indicators, such as failed logons by service accounts or changes in account creation and group membership initiated by these accounts, should be considered red flags warranting investigation. Additionally, the passage emphasizes specific events generated by certain services (e.g., MSIInstaller, Service Control Manager, and Volume Shadow Copy) that are associated with a service account as potential signs of compromise. These include: 1. Events related to failed logons, which might suggest an unauthorized attempt to authenticate using stolen credentials. 2. Changes in account creation and group membership by the service account, which could indicate further attempts to establish unauthorized access or persistence within the system. 3. Events from services like MSIInstaller (which tracks software installations), Service Control Manager (often targeted via PSExec for remote code execution), and Volume Shadow Copy (used to access domain databases) can signal an intrusion and are therefore important to monitor closely. By understanding these indicators and taking proactive measures to investigate suspicious activities, organizations can better protect their systems from credential theft and potential compromise by attackers using stolen service account credentials.

Disclaimer:

The content in this post is for informational and educational purposes only. It may reference technologies, configurations, or products that are outdated or no longer supported. If there are any comments or feedback, kindly leave a message and will be responded.