Firefox ESR Sandbox Escape: Critical CVE-2026-7321 Demands Immediate Attention
The National Vulnerability Database (NVD) has detailed CVE-2026-7321, a critical sandbox escape vulnerability within Firefox ESR’s WebRTC networking component. Rated with a CVSS score of 9.6, this flaw stems from incorrect boundary conditions, allowing attackers to potentially break out of the browser’s sandbox environment. This is a significant risk, as it could enable malicious code execution on the user’s system, bypassing intended security boundaries.
The NVD indicates that this vulnerability was patched in Firefox ESR version 140.10.1. The CVSS vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H highlights its exploitability over the network, requiring only user interaction (like visiting a malicious site), and its severe impact on confidentiality, integrity, and availability.
Defenders must prioritize patching affected Firefox ESR installations immediately. The attacker’s calculus here is straightforward: exploit a widespread browser vulnerability to gain a foothold on user machines, potentially leading to further compromise. Organizations should verify all endpoints are running the patched version and consider enhanced network monitoring for suspicious WebRTC-related traffic.
What This Means For You
- If your organization uses Firefox ESR, you must verify all installations are updated to version 140.10.1 or later immediately. This critical vulnerability allows for sandbox escapes, meaning an attacker could potentially execute code on user systems by tricking them into visiting a malicious website. Audit your systems for any unpatched instances and review logs for unusual WebRTC activity.
Related ATT&CK Techniques
🛡️ Detection Rules
4 rules · 6 SIEM formats4 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
Web Application Exploitation Attempt — CVE-2026-7321
title: Web Application Exploitation Attempt — CVE-2026-7321
id: scw-2026-04-28-1
status: experimental
level: high
description: |
Detects common exploitation patterns targeting web applications. Review CVE-2026-7321 advisories for specific indicators.
author: SCW Feed Engine (auto-generated)
date: 2026-04-28
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-7321/
tags:
- attack.initial_access
- attack.t1190
logsource:
category: webserver
detection:
selection:
cs-uri-query|contains:
- '..'
- 'SELECT'
- 'UNION'
- '<script'
- 'cmd='
- '/etc/passwd'
condition: selection
falsepositives:
- Legitimate activity from CVE-2026-7321
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-7321 | Sandbox Escape | WebRTC: Networking component |
| CVE-2026-7321 | Sandbox Escape | Firefox ESR < 140.10.1 |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | April 28, 2026 at 18:16 UTC |
This content was AI-rewritten and enriched by Shimi's Cyber World based on the original source. All intellectual property rights remain with the original author.
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