CVE-2026-14241: Mozilla Firefox RCE Vulnerability

CVE-2026-14241 Overview

CVE-2026-14241 identifies memory safety bugs in Mozilla Firefox 152.0.3. Several of the underlying defects showed evidence of memory corruption during Mozilla's internal testing. Mozilla assessed that a sufficiently motivated attacker could weaponize some of these bugs to run arbitrary code inside the browser process. The issue is tracked under the CWE-787 (Out-of-Bounds Write) weakness class and was resolved in Firefox 152.0.4. Mozilla published the fix in advisory MFSA-2026-62. Because Firefox routinely processes untrusted web content, the vulnerability is reachable through normal browsing activity without user interaction beyond visiting a crafted page.

Critical Impact
Successful exploitation may allow remote attackers to achieve arbitrary code execution in the context of the Firefox process by delivering crafted web content.

Affected Products

Mozilla Firefox 152.0.3
Earlier Firefox 152.x builds sharing the same code paths
Downstream distributions repackaging Firefox 152.0.3

Discovery Timeline

2026-06-30 - CVE-2026-14241 published to the National Vulnerability Database (NVD)
2026-07-01 - Last updated in NVD database
2026-07-02 - EPSS score recorded at 0.303% (percentile 22.005)

Technical Details for CVE-2026-14241

Vulnerability Analysis

The advisory groups multiple distinct memory safety defects reported against Firefox 152.0.3. Mozilla attributes these to the browser's internal fuzzing and code review process, with tracking bugs listed in the Mozilla Bugzilla Bug List and Mozilla Bug Report #2046814. Mozilla states that some of the reports demonstrated memory corruption during testing. The classification under [CWE-787] indicates that at least one path writes beyond the bounds of an allocated buffer. In a browser context, such writes can corrupt adjacent heap metadata, virtual method tables, or JIT-generated code regions.

Root Cause

The root cause is unsafe memory handling in native C/C++ components of Firefox. Out-of-bounds writes occur when input-driven size calculations or index computations bypass validation before touching heap or stack memory. Mozilla did not publicly disclose the affected subsystems at the individual bug level pending broader user updates.

Attack Vector

Exploitation is remote and requires no privileges or authentication. An attacker hosts crafted content on a web page and lures a user to visit it, or injects the content through a compromised advertisement or iframe. Rendering the content triggers the vulnerable code path in the browser process. Because the vulnerability lives in the content rendering stack, sandbox escapes would typically be chained separately to achieve broader system compromise.

No public proof-of-concept exploit is currently available, and CVE-2026-14241 is not listed on the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-14241

Indicators of Compromise

Unexpected Firefox process crashes with access violation or heap corruption signatures in Windows Error Reporting or macOS ReportCrash logs
Firefox child processes (plugin-container, content processes) spawning shells, powershell.exe, cmd.exe, or bash
Outbound connections from firefox.exe to newly registered or low-reputation domains immediately after page loads
Creation of persistence artifacts (registry Run keys, LaunchAgents, cron entries) by Firefox child processes

Detection Strategies

Inventory browser versions across the estate and flag any endpoints still running Firefox 152.0.3 or earlier 152.x builds
Alert on Firefox process crashes clustered by host, user, or visited URL, which can indicate exploitation attempts against the memory corruption bugs
Correlate web proxy logs with endpoint telemetry to identify users visiting suspicious pages followed by anomalous child process activity

Monitoring Recommendations

Forward browser crash telemetry and endpoint process events to a centralized analytics platform for correlation
Monitor for unsigned or unexpected code execution originating from the Firefox process tree
Track outbound network activity from browser processes to command-and-control indicators supplied by threat intelligence feeds

How to Mitigate CVE-2026-14241

Immediate Actions Required

Upgrade all Firefox installations to version 152.0.4 or later, which contains the fix from MFSA-2026-62
Enforce update policies through enterprise management (Group Policy, Intune, Jamf) so that browsers cannot remain on 152.0.3
Restrict browsing to trusted sites on any endpoint that cannot be immediately patched

Patch Information

Mozilla resolved CVE-2026-14241 in Firefox 152.0.4. Administrators should validate installed versions with firefox --version on Linux and macOS or by checking About Firefox in the browser. Mozilla's advisory MFSA-2026-62 lists all bugs bundled into the fix release.

Workarounds

Deploy web filtering to block access to untrusted or newly registered domains until patching completes
Enable strict site isolation and disable non-essential browser features such as JavaScript on high-risk profiles where operationally feasible
Route browser traffic through a secure web gateway that performs content inspection for known exploit patterns

bash

# Verify Firefox version and enforce update on Linux endpoints
firefox --version
# Expected output after remediation:
# Mozilla Firefox 152.0.4

# Trigger managed update via package manager (example: Debian/Ubuntu)
sudo apt-get update && sudo apt-get install --only-upgrade firefox