A password spraying attack is a type of cyber attack where an attacker uses a single password (or a list of commonly used passwords) against many different accounts before moving on to try a different password. This method is employed to avoid account lockouts that would normally occur from too many failed login attempts on a single account. Instead of targeting one user at a time with many passwords, the attacker sprays the same password across many users.

This technique takes advantage of the fact that many users might choose common, weak passwords like "password," "123456," or "qwerty." Since the attack is distributed across many accounts, it reduces the likelihood of triggering security mechanisms designed to detect and block multiple failed login attempts from a single IP address or against a single account. Password spraying is particularly effective against accounts where users have set weak passwords and where security settings do not enforce strong password policies or detect this type of attack pattern.

To protect against password spraying attacks, organizations and users should implement and adhere to strong password policies, enable multi-factor authentication (MFA) wherever possible, and monitor for unusual login attempts or patterns that could indicate a spraying attempt.

The Microsoft Incident

In January 2024, Microsoft revealed that it had fallen victim to an attack by Russian-state hackers known as Midnight Blizzard, Nobelium. The striking aspect of this breach was its simplicity; the attackers did not rely on sophisticated methods or exploit unknown vulnerabilities but instead utilized a straightforward password spray attack to compromise an old, unused account. The hackers executed the password spray attack in November 2023, employing a basic brute force strategy that attempts the same password across numerous accounts. Through the widespread application of weak and previously compromised passwords, they managed to infiltrate a non-production legacy test account within Microsoft's network. This access provided the necessary foothold to initiate their campaign, allowing either direct exploitation of this account's privileges or further privilege escalation.

For a duration of seven weeks, the attackers conducted operations that included the extraction of emails and document attachments, affecting a minimal fraction of Microsoft's corporate email accounts. Notably, this included accounts of individuals in senior management and members of the Cybersecurity and Legal departments. Upon detecting the breach on January 12th, Microsoft's Security team quickly intervened to halt the attackers' progress and prevent any further access, showcasing the ongoing battle between cybersecurity defenses and sophisticated hacker tactics.