Password spray attacks are a form of brute-force attack where an attacker attempts to gain unauthorised access to multiple accounts by using a few commonly used passwords. Unlike traditional brute-force attacks that target a single account with multiple password guesses, password spray attacks reverse this approach by using a small set of passwords across a large number of accounts. This technique allows attackers to evade account lockouts or alerts triggered by multiple failed login attempts on a single account, making it an effective, low-noise method for credential theft.

How Password Spray Attacks Work

In a password spray attack, attackers exploit a common vulnerability in many organisations: the use of weak or default passwords across multiple accounts. Here’s how it generally works:

• Account List Collection: The attacker collects or buys a list of usernames or emails from databases, social engineering, or data leaks.
• Low-Volume Testing: Instead of bombarding each account with numerous password attempts (which would trigger security alerts), the attacker tries a small set of common or likely passwords (e.g., "Password123", "Welcome1") across all accounts.
• Rotation and Obfuscation: To evade detection, attackers often use proxies or compromised networks to change IP addresses with each attempt. They also limit attempts to a few passwords per account each day.
• Gaining Access and Persistence: Once successful, attackers gain access to the account, allowing them to perform malicious activities like data exfiltration, privilege escalation, or internal reconnaissance.

Password spray attacks are highly effective because they exploit common, predictable password habits within organisations. They take advantage of employees using simple passwords or reusing passwords across different accounts.

Why Password Spray Attacks Are Dangerous

Password spray attacks are particularly concerning for a few reasons:

1. Evades Detection: Since the attack involves only a few login attempts per account, it often bypasses traditional security alerts and lockout policies.
2. Low-Cost, High-Reward: Attackers only need a handful of valid passwords to access sensitive accounts, making these attacks cost-effective.
3. Access to Critical Systems: If attackers gain access to administrative or high-privilege accounts, they can cause significant damage, steal sensitive information, and disrupt operations.

Examples of Password Spray Attacks

To better understand this type of attack, let’s look at some common tactics attackers use in password spray attacks:

Targeting Common Passwords Across Organizations: Attackers often try commonly used passwords, such as "Welcome123" or "Winter2024", which have a higher likelihood of success due to predictable password patterns in many organisations.

Using Seasonal or Event-Based Passwords: Attackers may use passwords relevant to current seasons, holidays, or events, such as “Spring2024” or “Football2024”, based on the assumption that users update passwords seasonally.

Compromised Router Networks for Masking Attempts: Attackers can use a network of compromised routers or IP addresses to rotate each login attempt. This helps them avoid detection and bypass location-based security filters, as seen in the CovertNetwork-1658 case, where Chinese threat actors used compromised routers to conduct password spray attacks.

Leveraging Leaked Credential Databases: Attackers may utilise publicly available databases of leaked credentials to focus on valid usernames and try a few common passwords, increasing their chances of success.

Real-World Incidents of Password Spray Attacks

Password spray attacks have been linked to various high-profile cybersecurity incidents, where attackers used this technique to access critical systems and sensitive data. Here are a few notable cases:

• Microsoft 365 Credential Theft (2021): The Russian threat group known as APT29 (or Cozy Bear) used password spray techniques to target Microsoft 365 accounts in the U.S. government and private sector. They targeted accounts with a few common passwords, gaining unauthorised access to email accounts and sensitive documents.
• Storm-0940 Attack on Microsoft Customers (2024): A Chinese threat actor, Storm-0940, used password spray attacks facilitated through CovertNetwork-1658, a network of compromised routers. This group leveraged these attacks to steal credentials and access systems across North American and European organisations, including government and private sectors.
• U.S. Energy Sector Attack (2019): A state-sponsored group launched a password spray attack targeting U.S. energy companies. They used common passwords to infiltrate industrial systems, demonstrating the vulnerability of critical infrastructure sectors to this kind of attack.
• Brute Ratel Attacks on Financial Institutions (2023): Attackers used Brute Ratel, a penetration testing tool, in combination with password spray techniques to target financial institutions. These attacks involved using commonly used passwords across different financial organisations, leading to data breaches and operational disruptions.
• Healthcare Sector Attacks by APT33 (2020): The Iranian-backed group APT33 conducted password spray attacks on healthcare organisations during the COVID-19 pandemic. Their goal was to gain access to research and sensitive data related to the pandemic, posing a threat to both data security and public health.

Password Complexity is Crucial: Organisations should enforce strong password policies that avoid common patterns and seasonal updates.

Multi-Factor Authentication (MFA): Implementing MFA can provide an additional security layer, even if attackers successfully guess the password.

Monitoring and Analytics: Advanced monitoring tools can help detect unusual login patterns, such as repeated attempts from different IPs or geographical locations.

Limit Account Exposure: Minimise the number of exposed accounts and disable unused accounts to reduce the attack surface.

User Education: Educate employees on the importance of unique, complex passwords and avoiding password reuse across personal and professional accounts.

Password spray attacks represent a significant threat to modern organisations, leveraging minimalistic but effective brute-force tactics that often go undetected. By targeting weak passwords across multiple accounts and masking attempts through covert networks, attackers can infiltrate sensitive systems with ease. Preventing these attacks requires a multi-layered security approach: enforcing complex password policies, deploying multi-factor authentication, and implementing advanced monitoring to detect suspicious activities.

Source and further reading.

ACSC releases advisory on password spraying attacks | CISA. (2019, August 8). Cybersecurity and Infrastructure Security Agency CISA. https://www.cisa.gov/news-events/alerts/2019/08/08/acsc-releases-advisory-password-spraying-attacks

Manager, D. P. |. S. T. (2024, October 17). How to defend against a password spraying attack. Semperis. https://www.semperis.com/blog/how-to-defend-against-password-spraying-attacks/

CSRC Content Editor. (n.d.). Brute Force password attack - Glossary | CSRC. https://csrc.nist.gov/glossary/term/brute_force_password_attack