Description

Internally found bugs present in Firefox 154, Firefox ESR 153.1, Firefox ESR 140.14 and Firefox ESR 115.39. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-09-01T13:20:08.673Z",
  "pubdate": "2026-09-01T13:20:08.673Z",
  "executiveSummary": "Mozilla has addressed multiple internally discovered vulnerabilities within the Firefox codebase, specifically impacting Firefox 154, Firefox ESR 153.1, Firefox ESR 140.14, and Firefox ESR 115.39. These vulnerabilities represent security-critical defects characterized by memory corruption or other unspecified security-relevant anomalies. While identified through internal auditing processes, the nature of these flaws suggests that, with sufficient technical effort, they could be weaponized to achieve arbitrary code execution or facilitate cross-site scripting/privilege escalation scenarios.\nThe inherent risk of memory corruption vulnerabilities involves the potential for an attacker to manipulate the process memory space, bypass browser sandbox protections, or execute arbitrary instructions under the security context of the application. These vulnerabilities do not explicitly require user authentication for exploitation, although successful execution typically relies on the user navigating to a malicious resource or interacting with crafted content. The affected versions cover both the standard release branch and Extended Support Releases (ESR), necessitating immediate remediation across the enterprise and consumer ecosystem. Users and administrators must update to the patched versions—Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, or Firefox ESR 153.2—to eliminate these attack vectors and maintain a secure browsing posture.",
  "technicalDetails": "The identified security defects involve memory corruption primitives residing within the core logic of Firefox 154, Firefox ESR 153.1, Firefox ESR 140.14, and Firefox ESR 115.39. Memory corruption vulnerabilities in browser environments typically stem from improper management of object lifecycles, leading to use-after-free (UAF) conditions, heap overflows, or out-of-bounds read/write access. These vulnerabilities occur when the browser's memory allocator or garbage collection mechanisms fail to properly synchronize state, allowing a malicious actor to maintain a reference to an object that has already been deallocated or is undergoing reallocation.\nExploitation of these memory-related defects generally follows a multi-stage attack flow. First, an attacker must deliver a malicious payload, often hosted on a compromised or malicious web domain, which interacts with the browser's rendering engine. By manipulating the Document Object Model (DOM) or specific JavaScript APIs, the attacker triggers the vulnerable code path—inducing a state of memory corruption. If successfully triggered, the attacker can leverage heap grooming techniques to replace the freed object with arbitrary data. This technique allows for the corruption of function pointers or virtual method tables (vtable), effectively hijacking the execution flow of the browser process.\nThe impact of such corruption is significant, as it enables the attacker to gain control over the instruction pointer. Given the sandbox architecture of Firefox, a successful exploit might initially result in code execution within the restricted content process. However, secondary vulnerabilities or architectural flaws could potentially be chained to escalate privileges, escape the sandbox, or gain persistent access to the host system. Because these vulnerabilities are inherent to the browser’s internal components, they require no prior authentication or administrative privileges on the part of the attacker. The primary requirement is the successful delivery and execution of a crafted payload within the target's browser environment, which can occur via standard web navigation or the consumption of untrusted dynamic content.\nThese security-relevant defects indicate failures in memory safety that the development team has rectified in the subsequent release cycle. The scope of the vulnerability spans the rendering pipeline and potentially the Just-In-Time (JIT) compilation modules or general object management components within the affected versions. By upgrading to the resolved versions—Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, or Firefox ESR 153.2—the integrity of the memory management subsystem is restored, mitigating the risk posed by potential exploits leveraging these specific corruption vectors."
}