Implementing Alert Fatigue Reduction

Quantify the problem before making changes:

--- Alert volume and disposition analysis (last 90 days)
index=notable earliest=-90d
| stats count AS total_alerts,
        sum(eval(if(status_label="Resolved - True Positive", 1, 0))) AS true_positives,
        sum(eval(if(status_label="Resolved - False Positive", 1, 0))) AS false_positives,
        sum(eval(if(status_label="Resolved - Benign", 1, 0))) AS benign,
        sum(eval(if(status_label="New" OR status_label="In Progress", 1, 0))) AS unresolved
  by rule_name
| eval fp_rate = round(false_positives / total_alerts * 100, 1)
| eval tp_rate = round(true_positives / total_alerts * 100, 1)
| eval signal_to_noise = round(true_positives / (false_positives + 0.01), 2)
| sort - total_alerts
| table rule_name, total_alerts, true_positives, false_positives, benign, fp_rate, tp_rate, signal_to_noise

--- Top 10 noisiest rules (candidates for tuning)
| search fp_rate > 70 OR total_alerts > 1000
| sort - false_positives
| head 10

Daily alert volume per analyst:

index=notable earliest=-30d
| bin _time span=1d
| stats count AS daily_alerts by _time
| stats avg(daily_alerts) AS avg_daily, max(daily_alerts) AS peak_daily,
        stdev(daily_alerts) AS stdev_daily
| eval alerts_per_analyst = round(avg_daily / 6, 0)  --- 6 analysts per shift
| eval capacity_status = case(
    alerts_per_analyst > 100, "CRITICAL — Exceeds analyst capacity",
    alerts_per_analyst > 50, "WARNING — Approaching capacity limits",
    1=1, "HEALTHY — Within manageable range"
  )

Step 2: Implement Risk-Based Alerting (RBA)

Convert threshold-based alerts to risk scoring in Splunk ES:

--- Instead of generating an alert for every failed login, contribute risk
--- Risk Rule: Failed Authentication (contributes to risk score, no alert)
index=wineventlog EventCode=4625
| stats count by src_ip, TargetUserName, ComputerName
| where count > 5
| eval risk_score = case(
    count > 50, 40,
    count > 20, 25,
    count > 10, 15,
    count > 5, 5
  )
| eval risk_object = src_ip
| eval risk_object_type = "system"
| eval risk_message = count." failed logins from ".src_ip." targeting ".TargetUserName
| collect index=risk

--- Risk Rule: Successful Login After Failures (additive risk)
index=wineventlog EventCode=4624 Logon_Type=3
| lookup risk_scores src_ip AS src_ip OUTPUT total_risk
| where total_risk > 0
| eval risk_score = 30
| eval risk_message = "Successful login after ".total_risk." risk points from ".src_ip
| collect index=risk

--- Risk Threshold Alert: Only alert when cumulative risk exceeds threshold
index=risk earliest=-24h
| stats sum(risk_score) AS total_risk, values(risk_message) AS risk_events,
        dc(source) AS contributing_rules by risk_object
| where total_risk >= 75
| eval urgency = case(
    total_risk >= 150, "critical",
    total_risk >= 100, "high",
    total_risk >= 75, "medium"
  )
--- This single alert replaces 10+ individual threshold alerts

Before RBA vs After RBA comparison:

BEFORE RBA:
  Rule: "Failed Login > 5"         → 847 alerts/day  (FP rate: 92%)
  Rule: "Suspicious Process"       → 234 alerts/day  (FP rate: 78%)
  Rule: "Network Anomaly"          → 156 alerts/day  (FP rate: 85%)
  Total: 1,237 alerts/day

AFTER RBA:
  Risk aggregation alerts           → 23 alerts/day   (FP rate: 18%)
  Each alert contains full context from multiple risk contributions
  Reduction: 98% fewer alerts with HIGHER true positive rate

Step 3: Tune High-Volume False Positive Rules

Systematically tune the noisiest rules:

--- Identify common false positive patterns
index=notable rule_name="Suspicious PowerShell Execution" status_label="Resolved - False Positive"
earliest=-90d
| stats count by src, dest, user, CommandLine
| sort - count
| head 20
--- Reveals: SCCM client generating 80% of false positives

Apply tuning:

--- Original rule (generating false positives)
index=sysmon EventCode=1 Image="*\\powershell.exe"
  (CommandLine="*-enc*" OR CommandLine="*-encodedcommand*" OR CommandLine="*invoke-expression*")
| where count > 0

--- Tuned rule (excluding known legitimate sources)
index=sysmon EventCode=1 Image="*\\powershell.exe"
  (CommandLine="*-enc*" OR CommandLine="*-encodedcommand*" OR CommandLine="*invoke-expression*")
  NOT [| inputlookup powershell_whitelist.csv | fields CommandLine_pattern]
  NOT (ParentImage="*\\ccmexec.exe" OR ParentImage="*\\sccm*")
  NOT (User="SYSTEM" AND ParentImage="*\\services.exe" AND
       CommandLine="*Microsoft\\ConfigMgr*")
| where count > 0

Document tuning decisions:

rule_name: Suspicious PowerShell Execution
tuning_date: 2024-03-15
original_fp_rate: 78%
tuned_fp_rate: 22%
exclusions_added:
  - ParentImage containing ccmexec.exe (SCCM client)
  - User=SYSTEM with ConfigMgr in CommandLine
  - Scheduled task: Windows Update PowerShell module
alerts_reduced: ~180/day eliminated
detection_impact: None — exclusions verified against ATT&CK test cases
approved_by: detection_engineering_lead

Step 4: Implement Alert Consolidation

Group related alerts into single incidents:

--- Consolidate alerts by source IP within time window
index=notable earliest=-1h
| sort _time
| dedup src, rule_name span=300
| stats count AS alert_count, values(rule_name) AS related_rules,
        earliest(_time) AS first_alert, latest(_time) AS last_alert
  by src
| where alert_count > 3
| eval consolidated_alert = src." triggered ".alert_count." related alerts: ".mvjoin(related_rules, ", ")

Splunk ES Notable Event Suppression:

--- Suppress duplicate alerts for the same source/dest pair within 1 hour
| notable
| dedup src, dest, rule_name span=3600

Step 5: Implement Tiered Alert Routing

Route alerts based on confidence and severity:

ALERT ROUTING STRATEGY
━━━━━━━━━━━━━━━━━━━━━
Tier 1 (Automated):
  - Risk score < 30: Auto-close with enrichment data logged
  - Known false positive patterns: Auto-suppress (reviewed quarterly)
  - Informational alerts: Route to dashboard only (no queue)

Tier 2 (Analyst Review):
  - Risk score 30-75: Standard triage queue
  - Medium confidence alerts: Analyst decision required
  - Enriched with automated context (VT, AbuseIPDB, asset info)

Tier 3 (Priority Investigation):
  - Risk score > 75: Immediate investigation
  - Deception alerts: Auto-escalate (zero false positive)
  - Known malware detection: Auto-contain + analyst review

Implement in Splunk:

index=notable
| eval routing = case(
    urgency="critical" OR source="deception", "TIER3_IMMEDIATE",
    urgency="high" AND risk_score > 75, "TIER3_IMMEDIATE",
    urgency="high" OR urgency="medium", "TIER2_STANDARD",
    urgency="low" AND fp_rate > 80, "TIER1_AUTO_CLOSE",
    1=1, "TIER2_STANDARD"
  )
| where routing != "TIER1_AUTO_CLOSE"  --- Auto-closed alerts removed from queue

Step 6: Measure Improvement and Maintain

Track alert fatigue metrics over time:

--- Weekly alert quality trend
index=notable earliest=-90d
| bin _time span=1w
| stats count AS total,
        sum(eval(if(status_label="Resolved - True Positive", 1, 0))) AS tp,
        sum(eval(if(status_label="Resolved - False Positive", 1, 0))) AS fp
  by _time
| eval tp_rate = round(tp / total * 100, 1)
| eval fp_rate = round(fp / total * 100, 1)
| eval alerts_per_analyst = round(total / 42, 0)  --- 6 analysts * 7 days
| table _time, total, tp, fp, tp_rate, fp_rate, alerts_per_analyst

Key Concepts

Tools & Systems

• Splunk ES Risk-Based Alerting: Framework converting individual detections into cumulative risk scores per entity
• Splunk ES Adaptive Response: Actions that can auto-close, suppress, or route alerts based on enrichment results
• Elastic Detection Rules: Built-in severity and risk score assignment with exception lists for tuning
• Chronicle SOAR: Google's SOAR platform with automated alert deduplication and grouping capabilities
• Tines: No-code SOAR platform enabling custom alert routing and automated enrichment workflows

Common Scenarios

• Post-RBA Implementation: Convert 15 threshold alerts into risk contributions, reducing daily volume by 85%
• Quarterly Tuning Cycle: Review top 20 noisiest rules, apply exclusions, measure FP rate improvement
• New Tool Deployment: After deploying new EDR, tune initial detection rules to baseline the environment
• Analyst Capacity Planning: Calculate optimal alert-to-analyst ratio (target 40-60 alerts/analyst/shift)
• Compliance Balance: Maintain detection coverage for compliance while reducing operational alert volume

Output Format

ALERT FATIGUE REDUCTION REPORT — Q1 2024
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Before (January 2024):
  Daily Alert Volume:     1,847
  Alerts/Analyst/Shift:   154
  False Positive Rate:    82%
  True Positive Rate:     8%
  Signal-to-Noise:        0.10
  Analyst Morale:         Low (2 resignations in Q4)

After (March 2024):
  Daily Alert Volume:     287 (-84%)
  Alerts/Analyst/Shift:   24
  False Positive Rate:    23% (-72% improvement)
  True Positive Rate:     41% (+413% improvement)
  Signal-to-Noise:        1.78

Changes Implemented:
  [1] Risk-Based Alerting deployed (15 rules converted)       -1,200 alerts/day
  [2] Top 10 noisy rules tuned with exclusion lists           -280 alerts/day
  [3] Alert consolidation (5-min dedup window)                -80 alerts/day
  [4] Tier 1 auto-close for low-confidence alerts             -N/A (removed from queue)

Detection Coverage Impact: NONE — ATT&CK coverage maintained at 67%
True Positive Detection Rate: IMPROVED — 12 additional true positives caught per week