CVE-2026-74969 in Firefox
Summary
by MITRE • 08/18/2026
Use-after-free in the Layout: Text and Fonts 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 classified as an out-of-bounds write due to use-after-free within the Layout: Text and Fonts component of Mozilla Firefox. This specific flaw occurs when the browser's rendering engine attempts to access or manipulate text layout data structures that have already been deallocated from memory. In complex web pages involving intricate typography, font substitution, or dynamic content reflowing, the internal state management may fail to properly synchronize object lifecycles with their references. Consequently, a pointer continues to reference a freed memory region, allowing subsequent operations to write data into this invalid location rather than allocating new safe memory for it.
From a technical perspective, use-after-free vulnerabilities are among the most dangerous classes of software defects because they provide attackers with significant control over program execution flow and memory layout. When an attacker can trigger the deallocation of an object while retaining a reference to it, they can manipulate what data is written into that freed space through crafted web content or malicious scripts. By carefully controlling the allocation patterns in adjacent memory regions, an adversary can overwrite critical function pointers, virtual table entries, or security cookies associated with other live objects. This mechanism effectively bypasses standard memory protection mechanisms such as Data Execution Prevention and Address Space Layout Randomization if exploited correctly, leading to arbitrary code execution within the context of the browser process.
The operational impact of this vulnerability is severe, potentially allowing a remote attacker to execute arbitrary code on the victim's system with the privileges of the user running Firefox. An attack would typically involve hosting or linking to a specially crafted webpage that triggers the specific sequence of font rendering and layout recalculations necessary to induce the use-after-free condition. Upon successful exploitation, the attacker gains full control over the browser process, which can serve as a foothold for further system compromise, including data theft, installation of malware, or pivoting to other systems on the network if additional vulnerabilities are present in connected applications.
Mitigation strategies primarily rely on timely software updates and defensive programming practices. Users must immediately upgrade to Firefox version 154, Firefox Extended Support Release (ESR) version 115.39, ESR version 140.14, or ESR version 153.1, as these releases contain the necessary patches that enforce proper reference counting and nullify dangling pointers after deallocation. For developers and security engineers analyzing similar issues in other software ecosystems, this incident aligns with CWE-416, which defines use-after-free errors, and maps to MITRE ATT&CK technique T1203, specifically the exploitation phase for client-side attacks. Implementing memory-safe languages or employing static analysis tools that detect dangling pointer usage can significantly reduce the risk of such vulnerabilities in future development cycles.