CVE-2026-14241: Firefox Remote Code Execution — Detection and Remediation Guide | Security Arsenal

Today, the NVD published CVE-2026-14241, a Critical (CVSS 9.8) vulnerability affecting Mozilla Firefox versions prior to 152.0.4. This issue is classified as a Network-exploitable memory safety bug that could allow an attacker to execute arbitrary code on a victim's machine simply by rendering a malicious web page.

Given the widespread deployment of Firefox in enterprise environments and the prevalence of web-based attack vectors, this vulnerability represents a high-risk pathway for initial access. Defenders must assume that proof-of-concept (PoC) exploit code will be available imminently and prioritize patching and detection logic immediately.

Technical Analysis

Affected Component: Firefox 152.0.3 Fixed Version: Firefox 152.0.4 CVE ID: CVE-2026-14241 CVSS Score: 9.8 (Critical) Attack Vector: Network (AV:N)

Vulnerability Mechanics

CVE-2026-14241 stems from memory safety bugs present in the Firefox 152.0.3 rendering engine. The advisory notes evidence of memory corruption, which typically manifests as use-after-free or buffer overflow conditions. In this context, the corruption occurs during the processing of web content.

From a defensive perspective, the attack chain is streamlined and efficient:

Delivery: The victim visits a malicious URL or a compromised legitimate website.
Exploitation: The browser's rendering engine mishandles memory objects while processing specific scripts or layout elements, triggering a corruption.
Execution: An attacker bypasses ASLR/DEP mitigations to gain control of the instruction pointer.
Payload: Arbitrary shellcode is executed within the context of the user's browser process.

Exploitation Status

While the advisory states that developers "presume" these bugs could be exploited to run arbitrary code, the CVSS 9.8 rating and the "Network" vector designation strongly suggest that reliable exploitation is feasible. In mature vulnerability management programs, a CVSS 9.8 in a client-side application is treated as an imminent threat equivalent to an active zero-day.

Detection & Response

Detecting the exploitation of browser-based memory corruption bugs requires identifying the effects of the exploit rather than the corruption itself (since standard EDRs do not monitor heap integrity). The most reliable signal is the parent browser process spawning unexpected child processes or loading suspicious in-memory modules.

The following rules and queries are designed to hunt for successful RCE attempts against Firefox or identify the presence of the vulnerable software version.

Sigma Rules

The following Sigma rule detects the primary post-exploitation behavior: Firefox spawning a shell or scripting engine.

YAML

---
title: Potential Firefox Remote Code Execution - Child Process Spawn
id: 8a4f2c19-9d3e-4b1c-8a5e-1f9d2e3c4b5a
status: experimental
description: Detects Firefox spawning suspicious child processes (cmd, powershell, wscript), which is highly indicative of successful code execution exploitation.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-14241
author: Security Arsenal
date: 2026/04/22
tags:
  - attack.execution
  - attack.t1204\logsource:
  category: process_creation
  product: windows
detection:
  selection_parent:
    ParentImage|endswith: '\firefox.exe'
  selection_child:
    Image|endswith:
      - '\cmd.exe'
      - '\powershell.exe'
      - '\pwsh.exe'
      - '\wscript.exe'
      - '\cscript.exe'
      - '\mshta.exe'
  condition: all of selection_*
falsepositives:
  - Legitimate user downloads triggering system prompts
  - Developer tools launching secondary processes
level: high
---
title: Detection of Vulnerable Firefox Version 152.0.3
id: 9b5g3d20-0e4f-5c2d-9b6f-2g0e3f4d5c6b
status: experimental
description: Identifies executions of the specific vulnerable Firefox version 152.0.3 to aid in asset inventory prioritization.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-14241
author: Security Arsenal
date: 2026/04/22
tags:
  - attack.initial_access
  - attack.t1189
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith: '\firefox.exe'
    ProductVersion: '152.0.3'
  condition: selection
falsepositives:
  - None
level: critical

KQL (Microsoft Sentinel / Defender)

This KQL query hunts for instances of the vulnerable process creation and suspicious child process relationships.

KQL — Microsoft Sentinel / Defender

// Hunt for Firefox 152.0.3 execution
DeviceProcessEvents
| where Timestamp > ago(7d)
| where FileName =~ "firefox.exe"
| where ProcessVersionInfoOriginalFileName =~ "firefox"
| extend FileVersion = ProcessVersionInfoProductVersion
| where FileVersion == "152.0.3"
| project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, FileVersion,FolderPath
| union (
    // Hunt for suspicious child processes spawned by Firefox
    DeviceProcessEvents
    | where Timestamp > ago(24h)
    | where InitiatingProcessFileName =~ "firefox.exe"
    | where FileName in~ ("cmd.exe", "powershell.exe", "pwsh.exe", "wscript.exe", "cscript.exe", "mshta.exe")
    | project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, FileName, CommandLine, SHA256
)

Velociraptor VQL

This VQL artifact hunts for the vulnerable binary on the disk and checks for currently running instances of the specific version.

VQL — Velociraptor

-- Hunt for vulnerable Firefox versions
SELECT
  OSPath,
  Mtime,
  Size,
  VersionInfo.ProductVersion AS Version
FROM glob(globs="/*ProgramFiles*/Mozilla Firefox/firefox.exe")
WHERE VersionInfo.ProductVersion = "152.0.3"

-- Check running processes
SELECT
  Pid,
  Name,
  Exe,
  Username,
  VersionInfo.ProductVersion AS RunningVersion
FROM pslist()
WHERE Name =~ "firefox"
  AND VersionInfo.ProductVersion = "152.0.3"

Remediation Script (PowerShell)

Use this script to audit your Windows endpoints for the vulnerable Firefox version. Note that administrative privileges are required to scan Program Files.

PowerShell

# Audit Script for CVE-2026-14241
# Checks for Firefox 152.0.3 installation

$VulnerableVersion = "152.0.3"
$FirefoxPaths = @(
    "${env:ProgramFiles}\Mozilla Firefox\firefox.exe",
    "${env:ProgramFiles(x86)}\Mozilla Firefox\firefox.exe"
)

Write-Host "[*] Starting Audit for CVE-2026-14241..."

foreach ($Path in $FirefoxPaths) {
    if (Test-Path $Path) {
        try {
            $VersionInfo = (Get-Item $Path).VersionInfo
            $FileVersion = $VersionInfo.ProductVersion
            
            Write-Host "[+] Firefox found at: $Path"
            Write-Host "    Installed Version: $FileVersion"
            
            if ($FileVersion -eq $VulnerableVersion) {
                Write-Host "[!] ALERT: Vulnerable version $VulnerableVersion detected." -ForegroundColor Red
                Write-Host "    Action Required: Update to Firefox 152.0.4 immediately."
            } elseif ($FileVersion -lt $VulnerableVersion) {
                Write-Host "[!] WARNING: Version is older than the vulnerable baseline. Update recommended." -ForegroundColor Yellow
            } else {
                Write-Host "[OK] Version is patched." -ForegroundColor Green
            }
        }
        catch {
            Write-Host "[-] Error reading version info for $Path" -ForegroundColor Red
        }
    } else {
        Write-Host "[-] Firefox not found at $Path"
    }
}

Remediation

The vendor has released an update to address this vulnerability. Defensive actions must be taken immediately.

1. Patch Management

SQL

Update all instances of Mozilla Firefox to **Version 152.0.4** or later.

Windows: Firefox should auto-update. Verify via Menu > Help > About Firefox.
Linux/macOS: Update via native package managers or download the latest build from Mozilla.

2. Vendor Advisory

Refer to the official advisory for release notes: https://nvd.nist.gov/vuln/detail/CVE-2026-14241

3. Risk Mitigation (If patching is delayed)

If immediate patching is not possible, enforce the following compensating controls:

Web Filtering: Block access to known malicious domains and uncategorized websites using secure web gateways (SWG).
Browser Isolation: Implement Remote Browser Isolation (RBI) for high-risk users to prevent rendering engine exploits from reaching the endpoint.
Application Control: Use AppLocker or Windows Defender Application Control (WDAC) to block firefox.exe from spawning cmd.exe, powershell.exe, or other binaries as defined in the detection rules.

Related Resources

Security Arsenal Penetration Testing Services AlertMonitor Platform Book a SOC Assessment vulnerability-management Intel Hub

CVE-2026-14241: Firefox Remote Code Execution — Detection and Remediation Guide