Medium RiskWindowsLegitimateCommonly Abused
firefox.exeWEB BROWSERfirefox.exe - Mozilla Firefox Browser Security Analysis
firefox.exe is the **Mozilla Firefox web browser**, a popular open-source browser. Attackers target Firefox for **credential theft** from stored passwords, **browser hijacking** via malicious extensions, and **data exfiltration** through the browser's network capabilities. Malware may also masquerade as firefox.exe or inject into its process.
Risk Summary
MEDIUM priority for SOC triage. firefox.exe is a legitimate browser that stores credentials and has extensive network access. Monitor for unexpected instances, unusual child processes (especially cmd.exe/powershell.exe), suspicious extensions, and profile data access outside normal browser operations.
Overview
What is firefox.exe?
firefox.exe is the main executable for Mozilla Firefox, an open-source web browser.
Core Functions
Web Browsing:
- Renders web pages
- Executes JavaScript
- Manages downloads
- Handles multimedia content
User Data Management:
- Stores passwords in logins.json (encrypted)
- Manages cookies and session data
- Stores browsing history
- Syncs data with Firefox Accounts
Security Significance
- Credential Storage: Encrypted password database
- Network Access: Legitimate outbound connections
- Extension System: Can be abused by malicious add-ons
- Profile Data: Valuable target for credential theft
Normal Behavior
Normal Behavior
Expected Process State
| Property | Expected Value |
|---|---|
| Path | C:\Program Files\Mozilla Firefox\firefox.exe |
| Parent | explorer.exe (user launch) |
| Instances | Multiple (multi-process architecture) |
| User | Logged-in user |
| Network | HTTP/HTTPS traffic |
| Children | firefox.exe (content processes) |
Multi-Process Architecture
firefox.exe (main/parent)
├── firefox.exe (GPU process)
├── firefox.exe (content process 1)
├── firefox.exe (content process 2)
└── firefox.exe (extension process)
Profile Location
%APPDATA%\Mozilla\Firefox\Profiles\*.default-release\
├── logins.json (encrypted passwords)
├── key4.db (encryption key)
├── cookies.sqlite
└── places.sqlite (history/bookmarks)
Common Locations
C:\Program Files\Mozilla Firefox\firefox.exeC:\Program Files (x86)\Mozilla Firefox\firefox.exeSuspicious Indicators
Legitimate vs Suspicious
LEGITIMATE
Path: C:\Program Files\Mozilla Firefox\firefox.exe
Parent: explorer.exe, firefox.exe
User: Logged-in user
Network: HTTPS to websites
Children: firefox.exe (content processes)
SUSPICIOUS
Path: C:\Users\Public\firefox.exe
C:\Temp\firefox.exe
Parent: cmd.exe, powershell.exe, wscript.exe
Children: cmd.exe, powershell.exe
Network: C2 destinations
Behavior: Accessing other user profiles
Warning Signs
| Indicator | Legitimate | Suspicious | Risk |
|---|---|---|---|
| Path | Program Files | Elsewhere | HIGH |
| Parent | explorer.exe | Script host | HIGH |
| Children | firefox.exe | cmd/powershell | CRITICAL |
| Profile Access | Own profile | Other profiles | HIGH |
Abuse Techniques
Attack Techniques
Technique #1: Credential Theft (T1555.003)
Targeting Firefox Passwords:
# Malware targets these files:
$profilePath = "$env:APPDATA\Mozilla\Firefox\Profiles\*.default*"
Copy-Item "$profilePath\logins.json" C:\exfil\
Copy-Item "$profilePath\key4.db" C:\exfil\
Tools Used:
- LaZagne
- Firefox Decrypt
- HackBrowserData
Technique #2: Malicious Extensions (T1176)
Extension-Based Attacks:
- Keyloggers disguised as extensions
- Form grabbers for credentials
- Browser history exfiltration
Detection:
# Check for suspicious extensions
Get-ChildItem "$env:APPDATA\Mozilla\Firefox\Profiles\*\extensions"
Technique #3: Process Injection (T1055)
Injecting into firefox.exe to:
- Intercept network traffic
- Steal credentials in memory
- Use browser as proxy
Technique #4: Process Masquerading (T1036.005)
Malware named firefox.exe in unexpected locations.
Detection Guidance
Detection Strategies
Priority #1: Unusual Child Processes
ParentProcess = "firefox.exe" AND
ChildProcess IN ["cmd.exe", "powershell.exe", "wscript.exe"]
→ ALERT: HIGH - Browser spawning shell
Sysmon Rule:
<RuleGroup groupRelation="and">
<ProcessCreate onmatch="include">
<ParentImage condition="end with">firefox.exe</ParentImage>
<Image condition="end with">cmd.exe</Image>
</ProcessCreate>
</RuleGroup>
Priority #2: Profile Data Access
Process != "firefox.exe" AND
FileAccess CONTAINS "Mozilla\Firefox\Profiles" AND
FileAccess CONTAINS ["logins.json", "key4.db"]
→ ALERT: CRITICAL - Credential theft attempt
Priority #3: Path Verification
Process = "firefox.exe" AND
Path NOT CONTAINS "Program Files"
→ ALERT: HIGH - Potential masquerading
PowerShell Check:
Get-Process firefox -ErrorAction SilentlyContinue | Where-Object {
$_.Path -notlike "*Program Files*"
} | ForEach-Object {
Write-Warning "Suspicious firefox.exe: $($_.Path)"
}
Remediation Steps
Protection and Remediation
Defense: Use Master Password
Enable Firefox Primary Password to encrypt credentials.
Defense: Extension Controls
Restrict extension installation via policies:
// policies.json
{
"policies": {
"ExtensionSettings": {
"*": {
"installation_mode": "blocked"
}
}
}
}
Defense: Profile Monitoring
Monitor access to Firefox profile directories.
If Compromise Suspected
- Check installed extensions
- Review profile for unauthorized access
- Change all stored passwords
- Clear cookies and sessions
- Check for injected DLLs
- Verify firefox.exe integrity
Investigation Checklist
Investigation Checklist
- Verify firefox.exe path is in Program Files
- Check for unusual child processes
- Review installed extensions
- Check for profile data access by other processes
- Examine network connections
- Review browser history for suspicious sites
- Check for DLL injection
- Validate file signature
MITRE ATT&CK Techniques
Last verified: January 18, 2026