What is Password Spraying

The success of password spraying comes from its alignment with how credentials are actually created and managed in real environments. Weak and patterned passwords remain common across organizations of any size. Large user populations rely on superficial seasonal variations, default onboarding credentials that are never changed, and company-based patterns. Another common widespread phenomenon is credential reuse of the same passwords across both personal and work accounts.

There are clear password policies meant to solve this problem of predictable passwords, but they, in fact, can reinforce the patterns, as requirements can be easily satisfied by constructions like “CommonWord1!” or predictable changes such as “CommonWord1” becoming “CommonWord2”. This behavior has led NIST to recommend against forced periodic password rotations.

There is a clear structural gap in how visible suspect authentication is when login attempts are distributed across many accounts and originate from different sources. Individual failures could resemble normal user behavior, and the main weakness is that account lockout policies operate per user, not across the environment. In reality, threshold-based controls are rarely triggered.

Password spraying is disproportionately effective against identity systems, and the reason is simple: in these environments, only one guessed password can unlock many other accounts.

In enterprise Active Directory, user credentials are the key to the domain, and the domain controls access to internal file shares, applications, and services. A valid account, even a low-privileged one, gives an attacker a legitimate foothold inside the network rather than at its edge.

Cloud identity providers such as Microsoft Entra ID, Google Workspace, and Okta are internet-facing by design, requiring a cloud security posture aligned with the CISA Cloud Security Technical Reference Architecture. They also sit at the center of an organization's application stack, as email, collaboration tools, HR systems, and business-critical SaaS platforms all authenticate through the same provider.

VPN gateways, OWA, RDP endpoints, and SSO portals have to stay publicly accessible to support remote work, which means they cannot be tucked away behind a perimeter. They are always there, always reachable. In federated environments, they tie back into the same centralized identity layer, so a successful spray on any one of them can open up access that goes well beyond what that single entry point would normally suggest.

Credential-based attacks are often grouped together, but they differ in how they distribute attempts and what the attacker already knows going in.

The spray itself is just the entry, as initial account takeover offers the attacker the appearance of a legitimate user based on the valid credentials obtained. The repercussions depend on what the compromised account exposes. The impact does not stay technical. Under regulations such as GDPR, HIPAA, and NIS2, a confirmed account compromise can trigger mandatory disclosure and regulatory scrutiny, along with long-term trust issues.

The technique used in advanced attacks remains the same; only more infrastructure and operational discipline are put behind it in sophisticated campaigns. Attempts are distributed, sometimes over thousands of compromised residential nodes, and each of them makes only one or two requests per account per day. The goal is simple: no source needs to generate enough volume to trigger an alert. The traffic comes from legitimate residential ISP ranges to pass IP reputation filtering.

Attention to detail is also greater. For instance, spray activity is within normal working hours in the target's time zone, like in the case of Peach Sandstorm, which limited its operations to 9 AM - 5 PM Iran Standard Time, making the traffic patterns look more regular.

When there is a higher level of planning, password lists are less generic and use breach data, more specific organizational naming conventions, and seasonal patterns relevant to the target sector. AI models trained on leaked credential datasets can surface statistically probable passwords far beyond what can be done through manual curation, which lead to AI and machine learning being increasingly used to automate this process. The same contextual intelligence is then reused after initial access to craft targeted follow-on attacks against higher-value accounts from the same environment.

After a password is guessed, the attacker might face an MFA and use repeated prompts to further the attack, sometimes in quick succession. The attacker might even follow up with a fake IT message or call, presenting it as a routine check and demanding confirmation.

When an account is validated, this often leads to further access attempts. Internal emails and contact patterns can then be used to approach other users, especially those with broader access.

For APT groups such as Midnight Blizzard, APT28, Peach Sandstorm, and Storm-0940, password spraying under T1110.003 is a deliberate initial access choice. The reasons are easy to deduce - this approach requires no exploit, leaves almost no forensic traces, and produces a valid credential attached to a session that looks entirely legitimate, which can be operationally extremely durable.

Detecting a password spray requires looking past individual login failures to identify a distributed pattern. Because these attacks are low-and-slow, the evidence is often scattered across thousands of log entries.

The primary IoC is a failure pattern noticeable across a broad set of usernames, with key signals such as:

• High-volume & low-frequency failures: Multiple accounts failing authentication within a specific window + each individual account only failing once or twice.
• Predictable credentials: The above failures are related to common passwords or organization-specific guesses.
• Infrastructure anomalies: Logins originating from unlikely sources,  geographically, known Tor exit nodes, or rotating residential proxies.
• MFA fatigue: A sudden spike in denied MFA prompts as users reject unauthorized access requests.
• Account activity: Disabled or service accounts that have not been active in months (dormant accounts) start displaying failed login attempts.

SIEM correlation logic aggregating telemetry across the identity stack is at the base of modern detection.

• Active Directory: Event ID 4625 (failed logon) and Event ID 4771 (Kerberos pre-auth failure) that appear across many distinct accounts when monitored can reveal password spraying. Considering that 4771 is not audited by default, Kerberos-based sprays can go undetected.
• Entra ID / M365: Analyze sign-in logs for error code 50126 across multiple accounts. Cases where authentication succeeded but was blocked by MFA or Conditional Access indicate a valid credential has already been guessed.
• UEBA and behavioral analytics: Distinguishes a spray from legitimate noise, such as a misconfigured VPN client or SSO retries after a password change.
• Honeypot accounts: Decoy accounts that appear legitimate but are never used by real employees provide a near-zero false-positive detection trigger.

If a spray is confirmed, the first 24 to 72 hours determine how far it spreads.

1. Block the source. Restrict the IPs involved at the firewall or WAF, knowing that distributed sprays often won’t rely on a single address.
2. Disable legacy authentication. Disable legacy authentication protocols such as POP3, IMAP, and Basic Auth. These paths do not enforce modern authentication controls and are frequently used in password spraying attempts.
3. Reset affected credentials. Any account that authenticated during the spray window should have its password reset and active sessions revoked.
4. Check earlier activity. Review recent logs as part of a retro hunt and look for signs that access was already used on affected accounts, such as forwarding rules, OAuth access, or new MFA devices.
5. User communication. Alert the workforce to report unexpected MFA prompts and treat any that were approved during the window as potentially compromised.

Password spraying can be best stopped by making a guessed password not enough. These are various ways to achieve this: