Most online services rely on passwords to secure user accounts, but attackers have ways to exploit weak passwords.
One such technique, password spraying, has become a persistent threat across many industries due to its low effort, relatively high success rate, and ability to evade detection.
In this article, we explain what password spraying is, how it works, and how you can detect and prevent it.
We’ll also look at real examples of password spraying attacks to understand their impact, and we’ll clarify how password spraying differs from other brute-force attacks.
By understanding this tactic, readers can better protect their accounts and systems from such attacks.
Password spraying is a type of brute-force cyberattack where an attacker tries a common password across many different user accounts.
In other words, instead of focusing on one account with many guesses, the attacker ‘sprays’ the same password on multiple accounts hoping one of them uses that password.
The goal is to find any account with a weak password, rather than breaking into a specific account.
This method is often called a ‘low-and-slow’ attack or a horizontal brute-force attack.
By spreading out password guesses across many accounts, the attacker avoids triggering IT security measures.
This includes things such as account lockouts that normally activate after a series of failed logins on one account.
For example, if a system locks an account after 5 wrong attempts, a typical brute-force attack would trip that limit quickly.
Password spraying evades this by only trying 1 or 2 guesses per account, flying under the radar of lockout policies.
It’s an opportunistic strategy that exploits the fact that some users choose extremely common passwords.
Security frameworks classify password spraying under brute-force attacks.
This isn’t because it’s fast, but because it relies on systematically guessing passwords to gain unauthorized access.
A password spraying attack usually unfolds in a few stages:
The attacker first compiles potential targets.
This could be a list of company email addresses or login usernames.
Often, finding usernames is easy thanks to predictable email formats or public information.
For example, many organisations use an email format like [email protected].
Attackers can guess or gather these from websites, social media, or data breaches.
In some cases, they might purchase usernames on the dark web.
Next, the attacker chooses a small set of very common or weak passwords.
These might be defaults or popularly used passwords such as ‘Password1’ or ‘Welcome123’.
Using automated tools or scripts, they then slowly try these passwords across all the usernames on the list.
Crucially, they limit the rate of attempts to avoid detection.
For instance, trying one password on each account, then pausing or rotating to the next password.
This approach means each account sees very few failed logins, so cybersecurity systems might not flag the activity.
Attackers often leverage password-spraying toolkits to streamline this process.
They may even spread attempts over hours or days to blend in with normal traffic.
Many password spraying attacks target widespread login services like email portals, VPNs, or single sign-on platforms.
This is because a successful login there can grant broad access.
If any account in the list uses one of the guessed passwords, the attacker gets in.
Even a single compromised account can be a foothold.
Once inside, the attacker might harvest sensitive data (like emails, files, or customer information) or use the account’s access to move deeper into systems.
They might access other applications the account has rights to, or even use the first account to phish for more credentials internally.
In a corporate environment, a successful password spray against a low-level user could still allow the attacker to escalate privileges or find information to target higher-value accounts.
Password spraying attacks have affected many well-known organisations.
Here are a few notable examples:
Between late 2018 and early 2019, attackers used password spraying to infiltrate Citrix’s internal network.
They succeeded in accessing the network and stole business documents and files from company drives and email accounts.
This incident forced Citrix to acknowledge that weak passwords had enabled unauthorised access to some of their systems.
In 2019, a group of attackers conducted a password spraying campaign targeting Microsoft Office 365 users.
They managed to compromise approximately 1,800 customer email accounts by using a list of commonly used passwords obtained from previous data breaches.
The attack highlighted how password spraying, combined with lists of leaked passwords, could lead to widespread email account breaches.
In 2023, the Russian state-backed hacking group known as APT28 (or ‘Fancy Bear’) carried out extensive password spraying attacks against Microsoft 365 accounts belonging to military and government organisations in Europe and North America.
The attackers carefully avoided detection by rotating their IP addresses and spreading login attempts over several weeks.
By not tripping any lockouts, they successfully breached some accounts and were able to spy on sensitive communications, such as defence-related emails.
This case showed how even well-secured environments could be tested by sophisticated adversaries using stealthy password spraying methods.
Detecting a password spraying attack can be challenging, because the activity is intentionally spread out and made to look like normal user logins.
However, there are several warning signs and patterns that can indicate a password spraying attempt is underway:
A sudden surge in failed login attempts across many different user accounts is a red flag.
For example, IT staff might notice an unusual number of accounts getting locked or showing failed logins around the same time.
No single account fails repeatedly enough to lock itself from retries, but many accounts show one or two failures.
This pattern is characteristic of password spraying.
Attackers often try logging in at times when legitimate users aren’t active.
If you see a wave of login attempts happening outside of normal business hours or from strange locations/IP addresses not typical for your users, it could indicate a spraying attack.
Logins coming from an overseas IP or at 3 AM for dozens of employees should raise suspicion.
An abnormal spike in network authentication traffic or bandwidth usage can also be a clue.
In log data, one telltale sign is the repeated use of one password across multiple accounts.
If the logs show that a particular password was attempted and failed for dozens of different usernames, that’s a strong indicator someone is password spraying.
In normal circumstances, different users wouldn’t all coincidentally mistype the same wrong password.
From a single user’s perspective, there may be signs your account was targeted.
Getting a password reset email or MFA prompt that you didn’t initiate could mean someone tried to access your account.
Additionally, if you do log in and see strange devices or locations in your account activity, these could be signs that an attacker briefly accessed your account.
While these user-side clues often appear after a successful compromise, they are important to notice and respond to quickly.
Protecting against password spraying requires a combination of good password usage and security measures that limit an attacker’s chances.
Key steps to prevent or mitigate these attacks include:
Ensure that all user accounts use complex passwords that are hard to guess.
Avoid simple or common passwords at all costs.
A good policy is to require a mix of uppercase and lowercase letters, numbers, and symbols for better security.
It’s also wise to check new passwords against lists of known breached or common passwords.
By eliminating weak passwords, you drastically reduce the chance that a password spraying attempt will hit a valid credential.
Implement account lockout rules or throttling mechanisms that activate after a certain number of failed login attempts.
For example, if an account sees five incorrect passwords in a row, you might lock it for 15 minutes or require a manual reset.
Even though password spraying tries to work around these limits, having them in place still helps.
It means an attacker can only try a small number of passwords per account before risking lockout.
Make sure any legacy systems or protocols are also covered, as attackers often look for unprotected login paths.
MFA is one of the most effective defences against password attacks.
Even if an attacker manages to guess a user’s password, they still cannot access the account.
Enabling MFA on all accounts greatly reduces the impact of password spraying.
It turns a guessed password from a total compromise into just a minor inconvenience.
Active monitoring can catch password spraying early.
Use security tools or logs to watch for unusual authentication patterns or spikes in failed logins across the board.
Set up alerts for these events so your security team gets notified of potential brute-force activity.
Modern analytics, including systems based on machine learning, can help identify the subtle patterns of a spray attack that might be missed by basic rules.
Once suspicious activity is detected, respond quickly by blocking the offending IPs, resetting affected accounts, or forcing additional verification steps.
Human factors are important too.
Teach users about the risks of weak passwords and encourage good practices.
Training users to recognise signs of account compromise and to report them can help catch an attack early.
While user awareness alone won’t stop a determined attacker, an informed user base adds an extra layer of defence.
Password spraying is essentially a kind of brute-force attack, but it works differently than the classic image of brute forcing.
In a traditional brute-force attack, a hacker picks one user account and rapidly tries a huge number of possible passwords for that account.
This could be done by cycling through dictionary words (a ‘dictionary attack’) or just attempting every combination of characters.
Such attacks tend to trigger defences quickly as most systems will lock an account or flag it after a handful of wrong password attempts in a row.
Brute-forcing a single account is noisy and usually only succeeds if no lockout policy exists.
It’s a ‘vertical’ approach’ – multiple passwords against one username.
Password spraying, on the other hand, is a ‘horizontal’ approach.
Instead of one account with many passwords, it’s many accounts with one password each.
This reversal is significant.
By spreading out the guesses, password spraying avoids the usual lockout triggers.
Each account sees so few attempts that it doesn’t trip the alarm.
But across the organisation the attacker may have tried hundreds of logins, just spread across different users.
Both classic brute force and spraying are trying to guess passwords, but spraying is sneakier in how it distributes the attempts.
It’s like trying one key on every door in a building, versus trying a bunch of keys on one door continuously.
Password spraying is a modern twist on the brute-force attack, with the use of common passwords across numerous accounts in an attempt to find a weak link.
This tactic has been leveraged in many high-profile breaches, demonstrating that even one easy password in an organisation can lead to serious consequences.
The good news is that defending against password spraying is very feasible.
Measures like enforcing strong, non-default passwords, enabling multi-factor authentication, monitoring login activity, and instituting account lockouts can collectively thwart the attack before it succeeds.
By staying vigilant and proactive, organisations and even individual users can significantly reduce the risk of a password spraying attack.
Remember that attackers are often looking for the easiest way in.
Eliminating that weakness goes a long way toward keeping accounts and data safe.