CVE-2026-74943 in Firefox
Summary
by MITRE • 08/18/2026
Use-after-free in the Graphics: ImageLib 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: ImageLib component of Mozilla Firefox, specifically classified as an use-after-free condition. This type of flaw occurs when software continues to reference a block of memory after it has been freed or deallocated by the system. In the context of browser-based rendering engines like ImageLib, which is responsible for decoding and displaying various image formats such as JPEG, PNG, GIF, and WebP, this error can be triggered during the processing of specially crafted media files. When an attacker provides a maliciously constructed image file to the victim, the application may allocate memory buffers to handle the image data but subsequently release those resources prematurely while internal pointers or references still retain access to that now-invalidated memory space.
From a technical perspective, this vulnerability falls under the Common Weakness Enumeration category CWE-416, which defines use-after-free as a situation where a pointer is used after it has been freed. The operational impact of such a flaw in a web browser environment is severe because browsers execute untrusted content from various websites and downloaded files with significant privileges relative to other applications on the user's system. If an attacker can control the contents of the memory that was previously allocated, they may be able to inject arbitrary code or manipulate data structures within the process. This manipulation often leads to a denial-of-service condition through application crashes but more critically allows for remote code execution with the privileges of the current user. The ability to execute arbitrary code enables attackers to install programs, view, change, or delete data, or create new accounts with full user rights on the affected system.
The exploitation vector typically aligns with ATT&CK techniques related to client-side attacks and memory corruption exploits. Attackers would likely distribute a malicious webpage containing an embedded image crafted to trigger this specific race condition or logic error within ImageLib. Upon loading the page, the browser processes the malformed data, leading to the premature deallocation of resources while active references remain in use. This scenario is particularly dangerous because it does not require user interaction beyond visiting a compromised site or opening a malicious email attachment containing an image file. The lack of immediate crash symptoms can sometimes allow for more sophisticated exploitation chains where the attacker gains persistent access to the victim's machine, potentially leading to further lateral movement within a network if the browser session is used as a foothold.
Mitigation strategies primarily rely on timely software updates and defensive configurations. Users must ensure that their Firefox installation is updated to version 154 or later for standard releases, or specifically to ESR versions 115.39, 140.14, or 153.1 as indicated in the security advisory. These patches contain code changes that properly manage memory lifecycles within ImageLib, ensuring that resources are only freed when all references have been safely released. In environments where immediate patching is not feasible due to compatibility concerns with legacy systems, network-level controls such as web filtering proxies can be configured to block access to known malicious domains or restrict the execution of scripts from untrusted sources. Additionally, enabling strict content security policies and disabling unnecessary browser features like automatic image loading for unknown origins can reduce the attack surface presented by this vulnerability. Security teams should also monitor endpoint detection systems for unusual memory allocation patterns indicative of exploitation attempts targeting browser processes.