CVE-2026-109718 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the XML component. This vulnerability was fixed in Firefox 158, Firefox ESR 115.43, and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified vulnerability represents a critical memory management error classified as an out-of-bounds write resulting from use-after-free conditions within the XML parsing component of Mozilla Firefox browsers. This specific class of flaw occurs when the application continues to reference a block of memory that has already been freed by the system, leading to unpredictable behavior and potential security breaches. In the context of web browser engines, such vulnerabilities are particularly dangerous because they reside in core components responsible for rendering complex document structures, making them attractive targets for attackers seeking to execute arbitrary code or escalate privileges on a victim's machine. The technical root cause typically involves a race condition or improper lifecycle management where an object is deallocated while still being referenced by another part of the application logic, such as during asynchronous XML processing events.
From a threat modeling perspective, this vulnerability aligns with CWE-416, which defines use-after-free errors that can lead to arbitrary code execution if exploited successfully. Attackers could potentially craft malicious web content containing specially formatted XML data designed to trigger the premature deallocation of memory structures while retaining active pointers within the browser's rendering pipeline. By manipulating these dangling pointers, an attacker might achieve control over program flow or overwrite critical data in memory, thereby bypassing modern security mitigations such as heap randomization and stack canaries that are standard in contemporary operating systems. The impact extends beyond simple application crashes to include potential remote code execution, allowing for the installation of malware, theft of sensitive credentials stored within the browser session, or complete compromise of the underlying host system depending on the user's privilege level.
The operational impact of this vulnerability is significant given Firefox's widespread adoption across enterprise and consumer environments. Users accessing compromised websites or those subjected to drive-by download attacks involving malicious XML payloads are at immediate risk until they update their software. The presence of such flaws in core parsing libraries means that even seemingly benign interactions with web pages can trigger the exploit chain if the attacker successfully engineers the timing and memory state required for the use-after-free condition to manifest. This underscores the importance of rigorous code review processes and automated fuzzing techniques during browser development cycles to detect these subtle logic errors before they reach production releases.
To mitigate this risk, organizations must ensure that all instances of Firefox are updated to version 158 or later, including specific maintenance releases such as Firefox ESR 115.43 and Firefox ESR 153.5 where the patch has been backported for long-term support users. Immediate deployment of these updates is critical to closing the attack surface associated with XML parsing operations. Additionally, security teams should enforce strict content security policies that restrict the loading of external resources and validate input data at application boundaries to reduce the likelihood of triggering such memory corruption bugs. Monitoring browser telemetry for unusual crashes or anomalies in XML processing can also serve as an early warning indicator of exploitation attempts in progress within the network environment.