🎯 Goal

The goal for today was to understand how authentication logs reveal brute-force and password-spraying attacks.

Authentication failures are one of the most common signals of intrusion attempts.

🛠 What I Did

Repeated authentication failures often indicate attack activity.

Common patterns include:

• brute-force attempts against a single account
• password spraying across many usernames
• credential stuffing from leaked databases

Learned to Differentiate Attack Types

Two common attack patterns appear in authentication logs.

Brute force:

many passwords → one user

Password spray:

one IP → many usernames

Understanding the difference is important when interpreting login failure data.

🔗 Key Cybersecurity Connections

Authentication attacks are extremely common in internet-exposed systems.

Security teams frequently monitor logs such as:

• SSH authentication logs
• Windows login events
• VPN authentication attempts

Grouping these events helps identify malicious activity.

🔍 Investigation Questions

When suspicious authentication activity appears in logs, investigators might ask:

Which IP address generated the login attempts?
How many failed login attempts occurred within a short time window?
Are multiple usernames targeted from the same IP address?
Are login attempts occurring against privileged accounts?
Are authentication failures followed by a successful login event?
Are the login attempts coming from geographically unusual locations?

These questions help analysts determine whether the pattern represents normal user behavior or a malicious authentication attack.

🚨 Detection Opportunities

Security teams can detect authentication attacks using several techniques:

alerting on high volumes of failed login attempts
detecting multiple usernames targeted from a single IP
identifying authentication attempts against many accounts in a short period
monitoring login attempts from new or suspicious geolocations
correlating authentication failures with subsequent successful logins

Telemetry sources used for detection include:

SSH authentication logs
Windows Event Logs (authentication events)
VPN login logs
identity provider logs.

🧭 MITRE ATT&CK Techniques

Authentication attacks commonly map to the following MITRE ATT&CK techniques:

T1110 — Brute Force
T1110.003 — Password Spraying
T1078 — Valid Accounts

These techniques describe how attackers attempt to gain unauthorized access by repeatedly testing credentials or abusing compromised accounts.

⚠ Challenges

Distinguishing Misconfiguration from Attack Activity

Some login failures occur due to:

• incorrect passwords
• outdated credentials
• automated system tasks

Investigators must analyze patterns rather than relying on single events.

📚 What I Learned

Aggregation reveals attack patterns

Individual authentication failures may appear harmless.

However, grouping events together often reveals clear signs of automated attacks.

➡ Next Steps

Future analysis will involve correlating authentication logs with:

• network connections
• process execution events

This helps determine whether attackers successfully gained access.

🧠 Reflection

Authentication logs provide valuable insight into external attack activity.

Learning to interpret these patterns is a fundamental SOC skill.

🧩 Lessons Learned

What worked

Analyzing repeated login failures quickly revealed suspicious patterns.

What broke

Single events were difficult to interpret in isolation.

Why it broke

Attacks become visible only when events are aggregated.

Fix / takeaway

Always group authentication events when investigating login activity.

📈 Skill Progression Context

Authentication log analysis is essential for roles such as:

• SOC Analyst
• Threat Hunter
• Incident Responder