CVE-2025-9182: Mozilla Firefox DoS Vulnerability

CVE-2025-9182 Overview

CVE-2025-9182 is a denial-of-service vulnerability caused by an out-of-memory condition in the Graphics: WebRender component of Mozilla Firefox and Thunderbird. This memory exhaustion vulnerability allows remote attackers to crash affected applications by triggering excessive memory allocation through specially crafted content that exploits improper resource consumption controls in the WebRender graphics rendering engine.

Critical Impact

This vulnerability enables remote attackers to cause denial-of-service conditions in Mozilla Firefox and Thunderbird by exhausting system memory through the WebRender graphics component, potentially disrupting user productivity and requiring application or system restart.

Affected Products

• Mozilla Firefox versions prior to 142
• Mozilla Firefox ESR versions prior to 140.2
• Mozilla Thunderbird versions prior to 142
• Mozilla Thunderbird ESR versions prior to 140.2

Discovery Timeline

• August 19, 2025 - CVE-2025-9182 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2025-9182

Vulnerability Analysis

This vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption) and affects the WebRender graphics rendering component used by Mozilla Firefox and Thunderbird. WebRender is Mozilla's GPU-based 2D rendering engine that handles the rendering of web content using the graphics hardware.

The vulnerability occurs when the WebRender component fails to properly limit memory allocation during graphics rendering operations. An attacker can exploit this by crafting malicious web content that forces the rendering engine to allocate excessive amounts of memory, ultimately leading to an out-of-memory condition that crashes the application.

The attack can be executed remotely over the network without requiring any privileges or user interaction beyond visiting a malicious webpage or viewing malicious email content. While the vulnerability does not compromise data confidentiality or integrity, it provides a reliable mechanism for disrupting application availability.

Root Cause

The root cause of CVE-2025-9182 lies in insufficient bounds checking and resource limits within the WebRender graphics component's memory allocation routines. The component fails to enforce proper constraints on the amount of memory that can be consumed during rendering operations, allowing malicious content to trigger unbounded memory allocation that exhausts available system resources.

Attack Vector

The attack vector for this vulnerability is network-based with low complexity. An attacker can exploit this vulnerability by:

1. Hosting malicious web content designed to trigger excessive memory allocation in the WebRender component
2. Directing victims to the malicious content through phishing links, malvertising, or compromised websites
3. For Thunderbird users, embedding the malicious content in HTML emails

When the victim's browser or email client attempts to render the malicious content, the WebRender component consumes memory until the system runs out, causing the application to crash. No authentication or special privileges are required for exploitation.

The vulnerability mechanism involves crafting graphical content that exploits the memory allocation behavior in WebRender's rendering pipeline. For detailed technical information, refer to the Mozilla Bug Report #1975837 and the associated security advisories.

Detection Methods for CVE-2025-9182

Indicators of Compromise

• Sudden, unexplained Firefox or Thunderbird crashes accompanied by high memory usage immediately before termination
• System logs showing memory allocation failures or out-of-memory errors associated with Firefox or Thunderbird processes
• Performance monitoring data revealing rapid memory consumption spikes in browser or email client processes
• Multiple users reporting simultaneous application crashes after visiting the same website or receiving the same email

Detection Strategies

• Implement endpoint monitoring to detect abnormal memory consumption patterns in Firefox and Thunderbird processes
• Deploy network security controls to identify and block access to known malicious domains serving exploit content
• Configure application crash reporting systems to correlate crashes with specific URLs or email sources
• Use SentinelOne's behavioral AI to detect resource exhaustion attack patterns targeting browser and email applications

Monitoring Recommendations

• Enable detailed crash reporting in Firefox and Thunderbird to capture diagnostic data when crashes occur
• Monitor system resource metrics (memory usage, page faults) for Firefox and Thunderbird processes in enterprise environments
• Implement centralized logging of browser navigation events to assist in post-incident investigation
• Review email gateway logs for suspicious HTML content patterns in conjunction with Thunderbird crashes

How to Mitigate CVE-2025-9182

Immediate Actions Required

• Update Mozilla Firefox to version 142 or later immediately
• Update Mozilla Firefox ESR to version 140.2 or later
• Update Mozilla Thunderbird to version 142 or later
• Update Mozilla Thunderbird ESR to version 140.2 or later
• Enable automatic updates to ensure timely deployment of future security patches

Patch Information

Mozilla has released security patches addressing this vulnerability in Firefox 142, Firefox ESR 140.2, Thunderbird 142, and Thunderbird 140.2. Organizations should prioritize updating to these versions to remediate the vulnerability. Official security advisories with detailed patch information are available:

• Mozilla Security Advisory MFSA-2025-64
• Mozilla Security Advisory MFSA-2025-67
• Mozilla Security Advisory MFSA-2025-70
• Mozilla Security Advisory MFSA-2025-72

Workarounds

• Consider disabling WebRender by setting gfx.webrender.all to false in about:config (note: this may impact rendering performance)
• Implement network-level blocking of known malicious domains distributing exploit content
• Configure email clients to display emails in plain text mode to prevent automatic HTML rendering in Thunderbird
• Use browser isolation solutions to contain potential exploitation attempts in sandboxed environments

# Firefox configuration to disable WebRender (temporary workaround)
# Navigate to about:config in Firefox and set:
# gfx.webrender.all = false
# gfx.webrender.enabled = false

# Alternatively, launch Firefox with WebRender disabled:
MOZ_WEBRENDER=0 firefox