Password guessing attacks are a critical cybersecurity threat. Active Directory (AD) environments are particularly susceptible, since a single compromised account can lead to widespread network infiltration. Thus, the consequences of password guessing attacks can be far-reaching and severe, leading to data breaches, network compromise, and significant operational disruptions. Privileged accounts require special attention, given their elevated access rights and the potential for extensive damage if compromised. Here’s what you need to know about password guessing and how to protect Active Directory—and your organization.
What is a password guessing attack?
Password guessing attacks are a form of cyber intrusion in which attackers systematically attempt a wide range of passwords to gain unauthorized access to systems. These attacks exploit the weakest link in security: human-chosen passwords. Despite advancements in cybersecurity, reliance on passwords as a primary authentication mechanism makes systems inherently vulnerable to these types of attacks.
Password guessing attacks exploit several types of vulnerabilities in Active Directory environments. Identifying and addressing these vulnerabilities is crucial in mitigating the risk of such attacks. The primary vulnerable targets include:
- User accounts with default or commonly used passwords. User accounts that are set up with default, common, or easily guessable passwords are a high risk. Such accounts include those that might have been created with a standard initial password that was never changed.
- Weak password policies. Accounts, especially those with elevated privileges, that are not governed by strong password policies are at significant risk. NIST and Microsoft both now recommend a minimum of 8 characters and the elimination of periodic password resets for user accounts, among other best practices. Weak password policies allow shorter, simpler, or predictable passwords and can significantly increase the risk of successful password guessing attacks. Unfortunately, few AD environments enforce common password rejection.
- Service accounts. Service accounts often have high-level permissions and are used to run applications, processes, or services within the network. The compromise of a service account can have widespread implications, as attackers can leverage the account’s permissions to access or disrupt critical services and processes.
The effectiveness of password guessing attacks is amplified when best practices for password security are not strictly followed—especially for administrative accounts.
Types of password guessing attacks
Password guessing attacks take various forms, each with unique characteristics.
Brute-force attacks
Brute-force attacks involve trying every possible password combination. Although time-consuming and resource-intensive, these attacks are surprisingly effective against accounts with simple or short passwords.
- The estimated time to brute-force a short (i.e., 6 or fewer characters), alphabet-only password can be as little as 5 minutes.
- Cracking alphanumeric combinations that include both upper- and lower-case characters might take around 5 hours.
- Complex alphanumeric combinations that include special characters can require about 8 days to crack.
Increasing the password length to 10 or more characters significantly reduces the likelihood of a successful brute-force attack, making it realistically impossible without the use of dedicated, special-purpose hardware.
Dictionary and password spraying attacks
In password spraying attacks and dictionary attacks, attackers use a list of common passwords and phrases. These lists often include variations and commonly used substitutions, exploiting the tendency of users to create passwords that are easy to remember.
- For a 6-character password, if the password is a common word or a simple variation, a dictionary attack can be very fast, potentially taking only minutes or hours. However, if the password is not in the dictionary or is more complex (e.g., a random combination of characters), the dictionary attack might not succeed at all.
- The likelihood of a dictionary attack’s success decreases even further with a 10-character password, especially when that password is a complicated or uncommon word or phrase. If the password is a common phrase or a combination of words, the attack might be feasible but would generally take longer than for a 6-character password.
Credential stuffing
Credential stuffing involves using known username and password pairs obtained from previous data breaches. This attack is particularly effective due to the common practice of password reuse across systems and services.
Password guessing attack risks
Password guessing attacks pose numerous risks and can have far-reaching consequences in Active Directory environments. The primary risk is unauthorized access, which can lead to a cascade of detrimental events:
- Data breaches. Successful password guessing attacks often result in data breaches, giving attackers access to sensitive information such as personal data, financial records, and intellectual property. This access not only harms organizational integrity but also can have legal and financial repercussions.
- Lateral movement. Once inside the network, attackers can use compromised credentials to move laterally across systems. Lateral movement enables threat actors to access other accounts, servers, or databases that are not directly reachable from the initial point of entry. Lateral movement is particularly dangerous in AD environments due to the interconnected nature of network resources.
- Privilege escalation. Attackers can exploit weak passwords to gain higher privileges within the network. This might involve compromising accounts with administrative privileges or escalating privileges of a lower-level account. Privilege escalation can lead to attackers gaining complete control over the network and its resources.
- Threat persistence. Attackers often aim to establish persistent access in the network, enabling them to return at will. They achieve this goal by creating backdoors, planting malware, or exploiting other vulnerabilities. Threat persistence in AD environments can be difficult to detect and eradicate without the proper tools.
- Operational disruption. Unauthorized access can disrupt business operations, leading to downtime, loss of productivity, and potential damage to the organization’s reputation.
- Compliance violations. Many industries and countries have regulations and standards governing data protection and privacy. Password guessing attacks that lead to data breaches can result in non-compliance, leading to fines and legal consequences.
Real-life incidents frequently involve attackers exploiting short or common passwords. For example, numerous data breaches have occurred because attackers were able to guess or crack simple passwords used by employees or administrators. In some cases, attackers have used compromised credentials to install ransomware, causing significant operational and financial damage.
How to detect password guessing attacks
Effective detection of password guessing attacks in Active Directory environments involves a multifaceted approach that combines monitoring, analysis, and the use of advanced security tools. Key strategies include:
- Monitoring login attempts. One of the primary indicators of a password guessing attack is an unusually high number of failed login attempts. Monitoring systems should be configured to alert administrators to excessive failed logins, especially when they occur in rapid succession or during unusual hours.
- Analyzing login patterns. Beyond the volume of login attempts, it is important to analyze the patterns of these attempts. This includes assessing login attempts from unusual locations, logins at atypical times, and logins to high-value or sensitive accounts. Such analysis can reveal more sophisticated password guessing attempts or instances where attackers might be using stolen credentials.
- Log-file analysis. Logs can provide detailed information about authentication attempts, including source IP addresses, timestamps, and user account details. Analyzing these logs can help identify potential password guessing activities and other suspicious behaviors. However, be aware that many attacks are adept at evading log-based detection.
- Network security tools. Use network security tools like intrusion detection systems (IDS), intrusion prevention systems (IPS), and security information and event management (SIEM) solutions. These tools can provide real-time analysis of network traffic and log data, helping to detect and alert on potential password guessing attacks—although again, they might not catch certain threats.
- Account-specific monitoring. Pay special attention to accounts that are known to be high-value targets, such as Domain Admin accounts.
- Endpoint protection. Implement endpoint protection solutions that can detect and alert on suspicious activities on individual workstations and servers. This includes monitoring for unusual processes or applications that might be indicative of a compromised account.
How to mitigate password guessing attacks
Responding to password guessing attacks in Active Directory environments requires a comprehensive approach that encompasses policy enforcement, user education, and technical controls.
Implement multifactor authentication and account lockout policies
Multifactor authentication (MFA) adds an additional layer of security by requiring a second form of verification beyond just the password. This can significantly reduce the risk of unauthorized access, even if a password is compromised.
Account lockout policies temporarily lock an account after a certain number of failed login attempts. This can help prevent brute-force attacks by limiting the number of guesses an attacker can make in a given period.
Comply with current password security guidelines
Adhering to guidelines set forth by agencies like NIST can enhance password security. This includes applying Fine-Grained Password Policies (FGPP) in AD, which enables you to apply different password policies to different groups of users, ensuring that privileged accounts have stricter requirements. All major password-manager providers include generators to help guide you.
Enforce robust password policies
Policies should mandate the use of complex passwords or passphrases that follow best practice guidance. The minimum password length ideally should be more than the traditional 8 characters, as longer passwords significantly increase the difficulty of password guessing attacks.
Passphrases are an even better option. These are generally longer and can be both more secure and easier to remember, thus reducing the likelihood of password reuse or simple, guessable passwords. Using a passphrase rather than a long, complex, and hard-to-remember password is recommended for several reasons, primarily revolving around the balance between security and memorability.
But action must be taken to enforce such policies. For example, consider banning common passwords. For environments that include Entra ID, Microsoft Entra Password Protection offers assistance with such steps. Third-party Active Directory password filters are also available to help you ban commonly used (and therefore commonly guessed) passwords.
Educate and train users
Conduct regular training sessions and awareness programs for all users, including those with privileged access. Educate them on the importance of password security, the risks of weak passwords, and best practices for creating strong, memorable passwords or passphrases.
Secure Active Directory and Entra ID
To effectively counter password guessing attacks in AD environments, administrators and cybersecurity specialists need to implement a range of proactive measures. Key actionable steps include:
- Conduct regular audits of user accounts and privileges. Ensure that accounts, especially those with elevated privileges, are granted only the access necessary for their roles and that any unnecessary permissions are revoked. Semperis’ free Purple Knight tool is a fast and simple way to detect excessive privileges and includes security indicators to detect privileged users with weak password policies and other risky password-related configurations.
- Automate monitoring and rollback. Monitor for signs of password guessing attacks, such as multiple failed login attempts, login attempts from unusual locations, or atypical access patterns. Ideally, use a tool that can detect stealthy attacks and attack patterns in AD and Entra ID and that provides the option to set up alerts and notifications or even roll back risky changes to Active Directory until you can confirm that they are legitimate.
- Plan for effective incident response. Develop and maintain an incident response plan that includes procedures for responding to suspected password guessing attacks. This plan should detail steps for containment, eradication, recovery, and post-incident identity forensics.
Semperis snapshot
Password guessing attacks in AD environments exploit misconfigurations and weak passwords, potentially leading to significant breaches and enabling lateral movement and privilege escalation. Understanding these risks and implementing targeted detection and mitigation strategies are crucial for safeguarding against these attacks.
Active Directory administrators and cybersecurity specialists must remain vigilant and proactively protect their networks from these pervasive threats. By implementing mitigation strategies, organizations can significantly reduce the risk of password guessing attacks and enhance the overall security of their AD environments.
