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Medium RiskWindows
peerblock.exeEXECUTABLE

PeerBlock - IP Blocking Firewall Application [2026]

PeerBlock is an IP blocking firewall used to block connections from specific IP ranges. May be abused to block security services, C2 blocklists, or evade network monitoring.

0viewsLast verified: Jan 18, 2025

Risk Summary

## Risk Summary | Factor | Assessment | |--------|------------| | Detection Difficulty | Low | | Abuse Potential | Medium | | Prevalence | Uncommon | | Risk Score | 45/100 | PeerBlock can be abused to block security services and evade detection.

Overview

What is peerblock.exe?

PeerBlock is a free, open-source IP blocking firewall that prevents connections to specified IP ranges.

Key Characteristics

AttributeValue
File Namepeerblock.exe
DeveloperPeerBlock Project
TypeFirewall/IP Blocker
LicenseOpen Source
Last UpdateLegacy (2014)

Technical Details

PropertyDescription
Process TypeUser Application/Service
MethodPacket filtering
ListsIP block lists (P2P, ads, etc.)
DriverKernel filter driver

PeerBlock was originally designed to block anti-P2P organizations but can block any IP ranges.

Normal Behavior

Normal Behavior

Legitimate Usage

peerblock.exe           # Launch application
pbfilter.sys            # Kernel driver

Expected Characteristics

AspectExpected Behavior
Parent Processexplorer.exe, services.exe
Driverpbfilter.sys loaded
User ContextUser or SYSTEM
NetworkList updates

Common Lists

List TypePurpose
P2P blocklistsBlock anti-piracy
AdvertisingBlock ad networks
SpywareBlock known bad IPs
CustomUser-defined

Common Locations

C:\Program Files\PeerBlock\peerblock.exeC:\Program Files (x86)\PeerBlock\peerblock.exe

Suspicious Indicators

Suspicious Indicators

Red Flags

IndicatorConcern LevelDescription
Blocking security IPsCriticalEvading protection
Blocking telemetryHighHiding activity
Enterprise deploymentHighPolicy violation
Attacker-deployedCriticalEvasion tool

Malicious Use Cases

Suspicious Blocking:
- Security vendor IPs blocked
- Windows Update blocked
- Telemetry endpoints blocked
- EDR cloud services blocked
- Threat intel feeds blocked

Attack Indicator

PatternConcern
Deployed post-compromiseEvasion setup
Custom blocking listsTargeted blocking
Blocking security vendorsDisabling protection

Abuse Techniques

Abuse Techniques

Security Evasion

Blocking Security Services:
1. Deploy PeerBlock on compromised system
2. Add security vendor IPs to block list
3. Block EDR cloud connections
4. Block Windows Defender updates
5. Malware operates undetected

C2 Protection

Protect C2 Traffic:
1. Install PeerBlock
2. Block threat intel IPs
3. Block reputation services
4. C2 traffic less likely flagged
5. Extends dwell time

Network Evasion

TechniqueImplementation
Block AV updatesPrevent signature updates
Block cloud AVDisable cloud scanning
Block telemetryHide activity
Block analystsPrevent investigation

Custom Block Lists

Attacker-Created Lists:
- Security vendor IP ranges
- Microsoft telemetry endpoints
- VirusTotal IP ranges
- Sandbox IP ranges
- Researcher networks

Detection Guidance

Detection Guidance

Sysmon Configuration

<RuleGroup name="PeerBlock Monitoring" groupRelation="or">
  <ProcessCreate onmatch="include">
    <Image condition="contains">peerblock</Image>
  </ProcessCreate>
  <DriverLoad onmatch="include">
    <ImageLoaded condition="contains">pbfilter</ImageLoaded>
  </DriverLoad>
</RuleGroup>

Sigma Rule

title: PeerBlock Execution
status: experimental
logsource:
  product: windows
  category: process_creation
detection:
  selection:
    Image|contains: 'peerblock'
  condition: selection
  falsepositives:
    - Privacy-conscious users
  level: medium

KQL Query

// PeerBlock execution
DeviceProcessEvents
| where FileName contains "peerblock"
| project Timestamp, DeviceName, ProcessCommandLine, AccountName

// PeerBlock driver load
DeviceDriverEvents
| where FileName contains "pbfilter"
| project Timestamp, DeviceName, FileName

Remediation Steps

Remediation Steps

Investigation

# Find PeerBlock
Get-ChildItem -Path C:\ -Recurse -Filter "peerblock.exe" -ErrorAction SilentlyContinue

# Check for driver
Get-WindowsDriver -Online | Where-Object { $_.OriginalFileName -like "*pbfilter*" }

# Check block lists
$listsPath = "$env:ProgramFiles\PeerBlock\lists"
if (Test-Path $listsPath) { Get-ChildItem $listsPath }

Removal

# Stop PeerBlock
Stop-Process -Name "peerblock" -Force

# Remove driver
sc.exe delete pbfilter

# Uninstall
# Use Add/Remove Programs or manual removal

Enterprise Controls

ControlImplementation
Application ControlBlock PeerBlock
Driver BlocklistBlock pbfilter.sys
Network MonitoringDetect blocking behavior

Investigation Checklist

Investigation Checklist

Deployment Analysis

  • When was PeerBlock installed?
  • Who installed it?
  • Is it authorized?
  • What version?

Block List Analysis

  • What lists are active?
  • Are security vendors blocked?
  • Any custom lists?
  • When were lists updated?

Impact Assessment

  • What IPs are blocked?
  • Security services affected?
  • Updates blocked?
  • Telemetry blocked?

Attack Correlation

  • Part of larger compromise?
  • Deployed by attacker?
  • Other evasion tools present?

MITRE ATT&CK Techniques

T1562.001 - Disable or Modify ToolsT1562.004 - Disable or Modify System Firewall