Full Report
Join Huntress Threat Hunters as they unpack the password-spraying techniques of threat actors, exposing how they target everything from small businesses to giants like Microsoft.
Analysis Summary
# Tool/Technique: Password Spraying (M365 Focus)
## Overview
Password spraying is a specialized type of brute-force attack where a threat actor attempts a small number of commonly used passwords (e.g., "Password123!") against a large volume of user accounts. Unlike traditional brute forcing, which targets one account with many passwords, password spraying targets many accounts with one (or few) passwords to evade account lockout policies and threshold-based detection.
## Technical Details
- **Type:** Technique (Sub-technique of Brute Force)
- **Platform:** Microsoft 365, Azure AD (Entra ID), SaaS platforms, and on-premises Active Directory.
- **Capabilities:** Credential discovery, initial access, and account takeover.
- **First Seen:** Continuous; notably highlighted in the January 2024 **Midnight Blizzard** attack on Microsoft.
## MITRE ATT&CK Mapping
- **[TA0001 - Initial Access]**
- **[T1078 - Valid Accounts]**
- **[TA0006 - Credential Access]**
- **[T1110 - Brute Force]**
- **[T1110.003 - Password Spraying]**
## Functionality
### Core Capabilities
- **Low and Slow Execution:** By trying only one password per account every few hours, attackers stay under the radar of automated blocking mechanisms.
- **Tenant Enumeration:** Identification of valid user accounts within a target Microsoft 365 tenant before initiating the spray.
- **Protocol Exploitation:** Targeting legacy authentication protocols (like POP3 or IMAP) that may lack Modern Authentication or Multi-Factor Authentication (MFA) enforcement.
### Advanced Features
- **Residential Proxy Integration:** Distributing login attempts across thousands of "clean" residential IP addresses to bypass IP-based reputation filtering and geo-blocking.
- **MFA Exhaustion (Push Spamming):** If a password is correct, attackers may repeatedly trigger MFA prompts to annoy the user into approving the request.
- **Legacy Tenant Targeting:** Specifically seeking out "orphaned" or legacy tenants that do not have the same security parity as the main production environment (as seen in the Midnight Blizzard case).
## Indicators of Compromise
- **File Hashes:** N/A (Technique-based, though specific tools like *o365spray* may have associated hashes).
- **File Names:** N/A
- **Registry Keys:** N/A
- **Network Indicators:**
- Logins from atypical ASNs (Autonomous System Numbers) associated with hosting providers or residential proxies.
- Multiple failed login attempts across *diverse* usernames originating from a single IP or a small range of IPs.
- **Behavioral Indicators:**
- A "horizontal" spike in failed logins (1 failure across 100 users) rather than a "vertical" spike (100 failures for 1 user).
- Successful logins followed immediately by the creation of new inbox rules or MFA device registrations.
## Associated Threat Actors
- **Midnight Blizzard (APT29 / Nobelium / SVR)**
- **LSHIY**
- **Various Phishing-as-a-Service (PhaaS) operators**
## Detection Methods
- **Behavioral Detection:**
- Monitoring M365 Sign-in logs for `ResultType 50126` (Invalid username or password) across multiple accounts within a short timeframe.
- Identifying "Impossible Travel" alerts coinciding with failed login attempts.
- **Log Analysis:** Correlating successful logins that occur after a series of failures across the wider tenant.
- **ASN Monitoring:** Flagging authentication attempts from non-standard or high-risk ASNs.
## Mitigation Strategies
- **Enforce Multi-Factor Authentication (MFA):** Implementation of phishing-resistant MFA (FIDO2) is the primary defense.
- **Disable Legacy Authentication:** Disabling POP3, IMAP, and SMTP Auth to force Modern Auth.
- **Conditional Access Policies:** Restricting logins based on location, device compliance, or risk score.
- **Password Policies:** Moving away from periodic password resets (which encourage weak, predictable passwords) toward long, unique passphrases.
## Related Tools/Techniques
- **Brute Force (T1110):** The parent technique involving exhaustive trial-and-error.
- **Credential Stuffing:** Using lists of compromised credentials from previous breaches.
- **Kali365 / Octopi365:** Phishing kits often used in conjunction with credential theft to bypass MFA.
- **o365spray:** A common open-source tool used to perform username enumeration and spraying against M365.