CVE-2026-2795: Mozilla Firefox Use-After-Free Vulnerability

CVE-2026-2795 Overview

A use-after-free vulnerability has been identified in the JavaScript Garbage Collection (GC) component of Mozilla Firefox and Thunderbird. This memory corruption flaw occurs when the JavaScript engine improperly manages memory during garbage collection operations, potentially allowing an attacker to reference freed memory objects.

Critical Impact
This vulnerability enables remote attackers to execute arbitrary code on affected systems by exploiting memory corruption in the JavaScript GC component, potentially leading to complete system compromise without requiring authentication or user interaction.

Affected Products

Mozilla Firefox versions prior to 148
Mozilla Thunderbird versions prior to 148

Discovery Timeline

2026-02-24 - CVE-2026-2795 published to NVD
2026-02-26 - Last updated in NVD database

Technical Details for CVE-2026-2795

Vulnerability Analysis

This use-after-free vulnerability (CWE-416) exists within the JavaScript Garbage Collection component of Mozilla's browser and email client applications. Use-after-free conditions occur when a program continues to use a pointer after the memory it references has been deallocated. In the context of JavaScript garbage collection, this can happen when objects are prematurely freed while still being referenced by other parts of the JavaScript engine.

The vulnerability is exploitable remotely over the network and requires no privileges or user interaction to trigger. An attacker could craft malicious JavaScript code that manipulates garbage collection timing to cause the use of freed memory. When successful, this can lead to arbitrary code execution within the context of the affected application.

Root Cause

The root cause stems from improper memory lifecycle management within the JavaScript GC component. During garbage collection cycles, the engine may incorrectly identify memory objects as unreferenced and free them while other components still maintain pointers to these objects. Subsequent access to these dangling pointers results in undefined behavior that attackers can exploit for code execution.

Attack Vector

The attack vector is network-based, requiring an attacker to deliver malicious JavaScript code to a victim's browser or email client. This can be accomplished through:

Malicious or compromised websites visited by Firefox users
HTML emails containing embedded JavaScript opened in Thunderbird
Malvertising campaigns that inject malicious scripts into legitimate advertising networks
Compromised web applications that serve attacker-controlled content

The vulnerability mechanism involves carefully crafted JavaScript that triggers specific garbage collection patterns to force use-after-free conditions. For detailed technical information, refer to the Mozilla Bug Report #2010940.

Detection Methods for CVE-2026-2795

Indicators of Compromise

Unexpected Firefox or Thunderbird process crashes, particularly those involving memory access violations
Suspicious child processes spawned from browser or email client applications
Unusual memory allocation patterns in JavaScript engine components
Network connections to unknown or malicious domains initiated by browser processes

Detection Strategies

Monitor for anomalous browser process behavior including unexpected code execution or child process creation
Deploy endpoint detection rules that identify memory corruption exploitation patterns
Implement network traffic analysis to detect delivery of known exploit payloads
Utilize browser crash reports to identify potential exploitation attempts targeting this vulnerability

Monitoring Recommendations

Enable enhanced logging for Firefox and Thunderbird application events
Monitor system process trees for suspicious activity originating from browser processes
Implement browser telemetry collection to identify unusual JavaScript execution patterns
Deploy SentinelOne agents configured to detect memory corruption exploitation techniques

How to Mitigate CVE-2026-2795

Immediate Actions Required

Update Mozilla Firefox to version 148 or later immediately
Update Mozilla Thunderbird to version 148 or later immediately
Enable automatic updates for all Mozilla products in enterprise environments
Consider temporary use of alternative browsers until patches can be deployed

Patch Information

Mozilla has released security patches addressing this vulnerability in Firefox 148 and Thunderbird 148. Organizations should prioritize deployment of these updates given the critical severity and network-exploitable nature of this vulnerability.

For official patch information and release notes, refer to:

Workarounds

Disable JavaScript execution in Firefox via about:config by setting javascript.enabled to false (note: this will break most modern websites)
Configure email clients to display messages in plain text mode rather than HTML
Implement web proxy filtering to block access to known malicious domains
Deploy network-level protections to inspect and filter malicious JavaScript content

bash

# Firefox configuration to disable JavaScript (temporary workaround)
# Navigate to about:config and set:
# javascript.enabled = false

# For enterprise deployment via policies.json:
{
  "policies": {
    "DisableJavaScript": true
  }
}