CVE-2026-118024 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the Graphics: Text component. This vulnerability was fixed in Firefox 159.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical memory management error classified as an out-of-bounds write, specifically manifesting through a use-after-free condition within the text rendering subsystem of Mozilla Firefox. In software architecture, particularly in complex graphical user interfaces like web browsers, components such as Graphics: Text are responsible for parsing font data, calculating glyph positions, and managing buffer allocations to render textual content accurately on screen. A use-after-free vulnerability occurs when the application continues to reference a memory block after it has been deallocated or freed by the system's garbage collector or explicit cleanup routines. In this specific context, the flaw likely stems from an inconsistency in how references to text layout objects are maintained during dynamic updates, such as when web pages modify their DOM structure or when CSS styles trigger reflows that alter text positioning and sizing dynamically.
From a technical perspective, the core issue lies in the lifecycle management of internal data structures used for text shaping and rendering. When a user navigates to a maliciously crafted webpage containing specific combinations of HTML elements, CSS properties, and JavaScript operations, the browser may attempt to access memory associated with a text object that has already been released. Because modern browsers operate on multi-process architectures where content runs in sandboxed processes, this vulnerability allows an attacker who controls the page content to write data into arbitrary memory locations within the Firefox process space. This out-of-bounds write capability is particularly dangerous because it can corrupt adjacent heap metadata or overwrite critical function pointers and object headers, leading to a loss of control over program execution flow.
The operational impact of this vulnerability extends beyond simple application crashes or denial of service conditions. While an attacker could theoretically trigger a crash by causing the browser to access invalid memory addresses, the primary risk associated with use-after-free vulnerabilities in web browsers is remote code execution. By carefully crafting heap spray techniques and exploiting specific alignment patterns within the freed memory chunks, an adversary can redirect the instruction pointer to execute arbitrary shellcode or native library functions. This effectively allows a malicious website to bypass browser security mitigations such as Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR), granting full control over the victim's system under the context of the user running Firefox. Such exploits are frequently utilized in drive-by download attacks where no further interaction from the user is required beyond visiting a compromised or maliciously hosted webpage.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-416, which defines use-after-free errors as situations where pointers do not check for null after memory deallocation or continue to reference freed memory blocks. Furthermore, in the context of the MITRE ATT&CK framework, this flaw facilitates techniques associated with Initial Access and Execution phases, specifically leveraging browser vulnerabilities to establish a foothold on an endpoint without user interaction beyond navigation. The exploitation chain typically involves constructing a malicious HTML document that triggers the specific rendering path leading to the premature deallocation of text-related objects while retaining active references within other parts of the layout engine or JavaScript runtime environment.
Mitigation for this vulnerability relies primarily on the immediate application of vendor-provided patches, as demonstrated by its resolution in Firefox version 159. Organizations and individual users should ensure that their browsers are updated to the latest stable release to incorporate fixes related to memory safety checks within the graphics and text subsystems. Additionally, defense-in-depth strategies such as enabling strict Content Security Policies (CSP) can help mitigate the impact of successful exploitation by restricting the sources from which scripts can be loaded and executed. For enterprise environments, deploying endpoint detection and response solutions that monitor for anomalous heap behavior or unexpected memory access patterns in browser processes can provide an additional layer of security against zero-day exploits targeting similar architectural flaws. Regular auditing of third-party plugins and extensions is also recommended to ensure they do not introduce conflicting behaviors with the core rendering engine's memory management routines.