CVE-2026-100786 in Firefox
Summary
by MITRE • 09/29/2026
Sandbox escape due to use-after-free in the Graphics component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
The identified security flaw represents a critical memory management error within the Mozilla Gecko rendering engine, specifically located in the Graphics subsystem responsible for handling visual data processing and display operations. This vulnerability is classified as an use-after-free condition, which occurs when software continues to reference a block of memory after it has been deallocated or freed by the system. In the context of browser-based environments, such errors are particularly dangerous because they can be triggered through maliciously crafted web content that interacts with graphics APIs like WebGL or Canvas elements. When an object is destroyed but pointers to its former location remain active in the application state, subsequent operations on those dangling pointers access invalid memory regions. This behavior violates fundamental principles of safe programming and creates a pathway for attackers to manipulate program execution flow by overwriting freed memory structures with controlled data payloads.
From a technical perspective, this flaw allows an attacker who successfully exploits the vulnerability to achieve arbitrary code execution within the context of the browser process. By carefully crafting input that triggers the premature deallocation of a graphics object while maintaining references to it, an adversary can overwrite adjacent heap metadata or function pointers. This manipulation enables the injection and subsequent execution of shellcode, effectively bypassing standard memory protection mechanisms such as Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR). The severity of this issue is compounded by its potential for sandbox escape, meaning that an attacker could break out of the restricted browser security container to interact with the underlying operating system. This transition from a web context to local system access represents a significant escalation in threat capability, allowing for full compromise of the victim's machine including theft of sensitive data, installation of persistent malware, or use as part of a botnet.
The operational impact of this vulnerability is severe due to its prevalence and ease of exploitation via standard web browsing activities. Users visiting compromised websites or pages containing maliciously crafted graphics content could trigger the flaw without any additional interaction beyond normal page rendering. The lack of user intervention required for exploitation increases the risk profile significantly, as automated drive-by download techniques can leverage this weakness silently in the background. Furthermore, because the Graphics component is integral to modern web applications that rely heavily on visual processing, the attack surface remains broad across various types of websites including those utilizing complex animations, 3D rendering, or video playback features. The vulnerability affects multiple versions of Firefox and its Extended Support Release (ESR) branches, indicating a systemic issue in the codebase that persisted until specific patches were applied to version ESR 153.4, standard release 157, ESR 115.42, and ESR 140.17.
Mitigation strategies primarily involve ensuring all Firefox installations are updated to include these security fixes immediately upon availability. For enterprise environments utilizing Extended Support Releases, it is critical to verify that the patching cycle aligns with Mozilla’s release schedule for ESR versions to maintain a secure posture against known exploits. Additionally, organizations should enforce strict content security policies and deploy browser isolation technologies such as sandboxed browsing profiles or virtual desktop infrastructure to limit the potential impact of any successful exploitation attempt. Security awareness training can also help reduce risk by discouraging interaction with untrusted web sources that may contain malicious graphics payloads. Monitoring for anomalous behavior in system processes, particularly those related to memory allocation and deallocation patterns, can aid in detecting attempted exploits before they result in full compromise.
This vulnerability aligns with Common Weakness Enumeration (CWE) identifier CWE-416, which describes use-after-free conditions as a distinct class of software defects leading to undefined behavior and potential security breaches. In terms of the MITRE ATT&CK framework, this flaw facilitates techniques associated with initial access through drive-by compromise and privilege escalation via sandbox escape mechanisms like T1055 or related process injection methods. Understanding these mappings helps in categorizing the threat within broader cybersecurity defense models and informs the development of detection rules based on behavioral indicators rather than just signature-based matching. Continuous monitoring for memory corruption anomalies and maintaining up-to-date software configurations remain essential components of a robust security strategy against such high-severity vulnerabilities.