CVE-2026-74940 in Firefox
Summary
by MITRE • 08/18/2026
Use-after-free in the Graphics: Text component. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
The identified vulnerability represents a critical memory management error within the Graphics Text component of Mozilla Firefox, specifically classified as an use-after-free condition. This type of flaw occurs when software continues to reference a pointer after the memory it points to has been deallocated or freed by the system. In the context of browser rendering engines, this typically involves complex interactions between text layout algorithms and graphics acceleration layers where objects are created, rendered, and then destroyed during dynamic page updates or scrolling operations. When an object is prematurely released while still being referenced by another part of the application, such as a pending render task or a callback function, the program attempts to access invalid memory addresses. This behavior violates fundamental principles of safe memory management and introduces significant instability into the browser's execution environment.
From a technical perspective, this vulnerability falls under CWE-416, which defines use-after-free errors where pointers are used after they have been freed. The attack surface is particularly dangerous because modern browsers execute untrusted web content in sandboxed processes to mitigate risks. However, sophisticated memory corruption vulnerabilities like this one can often bypass these sandboxes if the exploit chain successfully achieves arbitrary code execution before the operating system's security mechanisms intervene. An attacker could craft a malicious webpage containing specially designed JavaScript and HTML that triggers the specific sequence of events leading to the premature deallocation of text-related graphics objects. By carefully controlling memory allocation patterns, an adversary might overwrite freed memory with controlled data, thereby gaining control over program flow or reading sensitive information from adjacent memory regions.
The operational impact of this vulnerability is severe, potentially allowing remote attackers to execute arbitrary code on a victim's system simply by visiting a compromised website. This aligns with the MITRE ATT&CK technique T1203, which covers exploitation for client-side execution. If exploited successfully, the consequences extend beyond mere application crashes or denial of service. The attacker could establish persistence, exfiltrate sensitive data such as cookies and session tokens, or use the compromised browser instance to pivot into other parts of the network infrastructure. Given that Firefox is a widely used web browser with millions of daily active users across various operating systems including Windows, macOS, Linux, Android, and iOS, the potential blast radius of this vulnerability is substantial. Users relying on older versions are exposed to these risks without any protective measures in place.
To mitigate the risk associated with this use-after-free flaw, it is imperative that all affected environments be updated immediately. The issue was resolved in Firefox version 154 as well as specific Extended Support Release (ESR) branches including ESR 115.39, ESR 140.14, and ESR 153.1. Organizations should enforce automated update policies to ensure that all client machines running Firefox are patched against this vulnerability. For users who cannot immediately upgrade due to compatibility constraints with legacy applications, alternative mitigation strategies include restricting web browsing privileges through application whitelisting or deploying network-level security controls such as Web Application Firewalls (WAFs) and intrusion prevention systems that can detect and block known exploit patterns associated with memory corruption attacks in browser traffic. Regular vulnerability scanning and patch management cycles are essential to maintaining a secure posture against evolving threats targeting common software components like graphics rendering engines.