CVE-2026-118009 in Firefox
Summary
by MITRE • 10/27/2026
Integer overflow, use-after-free in the Graphics: Text component. This vulnerability was fixed in Firefox 159.
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Analysis
by VulDB Data Team • 10/27/2026
The identified security flaw resides within the text rendering subsystem of Mozilla Firefox, specifically affecting the Graphics: Text component. This area of the browser engine is responsible for converting Unicode character data into visual glyphs on the display surface, a process that involves complex memory management and arithmetic calculations to determine layout metrics such as width, height, and positioning coordinates. The vulnerability manifests in two distinct but potentially compounding forms: an integer overflow and a use-after-free condition. These defects represent critical failures in input validation and memory lifecycle management within the core rendering pipeline.
The integer overflow aspect of this vulnerability typically arises when arithmetic operations involving text metrics or buffer sizes exceed the maximum value that can be represented by the allocated data type, such as a 32-bit signed integer. In the context of graphics processing, miscalculations in dimensions or offsets can lead to incorrect memory allocation requests or out-of-bounds array indexing. When an attacker supplies crafted input containing specific Unicode sequences or extreme font metrics, the browser may compute negative values or wrap-around integers for buffer sizes. This miscomputation allows subsequent operations to access memory regions outside the intended boundaries of the allocated object, leading to heap corruption or arbitrary read/write capabilities depending on how the overflowed value is utilized in downstream rendering functions.
Concurrently, the use-after-free vulnerability indicates a failure in tracking the lifetime of dynamically allocated objects within the text layout engine. This condition occurs when the application continues to reference memory that has already been deallocated and potentially reused for other purposes. In the Graphics: Text component, this could happen if an object representing a glyph run or font face is freed while still being referenced by another part of the rendering pipeline, such as during asynchronous updates or complex text shaping operations involving OpenType features. An attacker who can trigger specific sequences of text layout calculations might exploit this race condition to execute arbitrary code with the privileges of the browser process. The combination of these two flaws creates a high-severity attack vector where memory corruption is facilitated by incorrect arithmetic, leading to potential remote code execution upon visiting a specially crafted webpage.
From an industry standard perspective, this vulnerability aligns closely with CWE-190 (Integer Overflow or Wraparound) and CWE-416 (Use After Free). These classifications highlight the fundamental weaknesses in input validation and memory management that allowed the exploit to succeed. In terms of adversary tactics, this flaw maps to MITRE ATT&CK techniques related to initial exploitation via browser vulnerabilities, specifically leveraging client-side code execution through crafted web content. The attack vector is primarily remote, requiring a user to visit a maliciously constructed site or open a document with embedded complex text rendering requirements that trigger the faulty logic within the Firefox engine.
The operational impact of this vulnerability is severe, as successful exploitation could allow an attacker to bypass security sandboxing mechanisms and execute arbitrary code on the victim's system. This compromises the confidentiality, integrity, and availability of user data and system resources. Given that browser engines process untrusted content from the web daily, such vulnerabilities pose a significant risk to widespread user bases if left unfixed. The presence of both integer overflow and use-after-free conditions suggests deep-seated issues in how the text component handles edge cases involving complex scripts or unusual font configurations, which are common targets for fuzzing-based exploitation attempts.
To mitigate this risk, users must ensure that Mozilla Firefox is updated to version 159 or later, where these specific defects have been addressed by the development team. The fix likely involves implementing stricter bounds checking on integer arithmetic operations related to text metrics and enhancing reference counting mechanisms to prevent premature deallocation of graphics objects. Additionally, developers should review similar code paths in the rendering engine for analogous patterns that could lead to memory safety violations. For organizations deploying Firefox at scale, enforcing automatic update policies is critical to ensure all endpoints are protected against this class of vulnerabilities. Security teams should also monitor for emerging exploit kits that may target older versions of browsers lacking these patches, as such exploits often appear shortly after public disclosure or patch release dates.