BURSTMozilla has released Firefox 139.0.4 to address critical security vulnerabilities that could potentially cause browser crashes and compromise user security.
These high-impact vulnerabilities CVE-2025-49709 and CVE-2025-49710 exploit fundamental components of Firefox’s graphics rendering system and JavaScript engine, respectively, posing risks ranging from abrupt browser crashes to potential remote code execution.
Critical Memory Corruption Vulnerability (CVE-2025-49709)
The first vulnerability, designated as CVE-2025-49709, represents a significant security concern within Firefox’s canvas rendering system.
Security researcher Yannis Juglaret discovered that certain Canvas operations could lead to memory corruption, a dangerous condition that can result in unpredictable browser behavior, crashes, or potentially exploitable security breaches.
The vulnerability specifically affects how Firefox handles canvas surfaces, which are fundamental components used for rendering graphics, animations, and interactive visual elements on web pages.
Memory corruption vulnerabilities are particularly concerning because they can allow malicious actors to potentially execute arbitrary code or cause denial-of-service attacks.
When canvas operations trigger memory corruption, the browser’s memory management system becomes compromised, leading to data integrity issues that can cascade into broader system instability.
Canvas elements are ubiquitous in modern web applications, making this vulnerability especially significant for users who frequently interact with graphics-intensive websites, online games, or web-based design tools.
JavaScript Engine Integer Overflow (CVE-2025-49710)
The second critical vulnerability, CVE-2025-49710, affects Firefox’s JavaScript execution environment through an integer overflow in the OrderedHashTable data structure.
Discovered by security researcher Shaheen Fazim, this flaw poses substantial risks to browser stability and security.
The OrderedHashTable is a crucial component of Firefox’s JavaScript engine, responsible for managing data structures that maintain insertion order while providing efficient lookup capabilities.
This makes it fundamental to JavaScript’s Map and Set objects, which are extensively used in modern web applications.
When an integer overflow occurs in this context, it can lead to memory allocation errors, incorrect data handling, or potentially exploitable conditions that malicious websites could leverage.
| CVEs | Affected Products | Impact | Exploit Prerequisites | CVSS 3.1 Score |
| CVE-2025-49709 | Firefox < 139.0.4 | Arbitrary memory corruption | User loads malicious webpage with crafted canvas operations | 8.8 (High) |
| CVE-2025-49710 | Firefox < 139.0.4 | Heap Buffer Overflow | User interacts with JavaScript-heavy malicious site | 8.6 (High) |
User Recommendations
Mozilla’s rapid response to these vulnerabilities demonstrates the organization’s commitment to maintaining Firefox’s security posture.
The company classified both vulnerabilities as high impact, reflecting their potential to significantly affect user security and browser functionality.
Firefox 139.0.4 includes comprehensive patches that address the underlying causes of both memory corruption and integer overflow issues without compromising browser performance or compatibility.
Users are strongly encouraged to update to Firefox 139.0.4 immediately to protect against potential exploitation of these vulnerabilities.
The update process can be initiated through Firefox’s built-in update mechanism or by downloading the latest version directly from Mozilla’s official website.
System administrators in enterprise environments should prioritize deploying this update across their organizations to maintain security compliance and protect against potential attacks targeting these specific vulnerabilities.
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