CVE-2026-74987 in Firefox
Summary
by MITRE • 08/18/2026
Internally found bugs present in Firefox ESR 140.13, Firefox ESR 153.0 and Firefox 153. 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 154, Firefox ESR 140.14, and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/19/2026
The identified vulnerabilities reside within the core architecture of Mozilla Firefox, specifically affecting versions 140.13 Extended Support Release (ESR), 153.0 ESR, and version 153 standard release. These issues were discovered through internal quality assurance processes rather than external reporting, indicating a proactive approach to security hygiene by the development team. The nature of these defects is characterized as memory corruption or other security-relevant anomalies that compromise the integrity of the browser's execution environment. Memory corruption vulnerabilities are particularly critical in web browsers because they often serve as the foundational primitive for more complex attack chains, including arbitrary code execution and privilege escalation attacks against the host operating system.
From a technical perspective, memory corruption typically involves violations such as buffer overflows, use-after-free conditions, or heap spraying techniques that allow an attacker to manipulate how data is stored and accessed in memory. When these flaws are present, they can lead to undefined behavior during rendering processes or JavaScript execution. Although the specific exploitability of each individual bug was not confirmed through external proof-of-concept code, the presence of memory corruption indicators strongly suggests that with sufficient effort and reverse engineering by a determined adversary, these defects could be leveraged to execute malicious payloads. This presumption aligns with historical patterns where internal findings often precede public exploitation campaigns targeting widely deployed software like Firefox.
The operational impact of these vulnerabilities is significant due to the widespread adoption of Firefox across enterprise environments that rely on ESR versions for stability and long-term support. An attacker could potentially craft a malicious webpage or modify an existing site to trigger these memory corruption flaws when visited by a user running the affected browser versions. Successful exploitation would likely result in remote code execution, allowing the adversary to gain control over the victim's system with the privileges of the current user. This poses severe risks including data theft, installation of persistent malware, and use of the compromised machine as part of a botnet or for lateral movement within corporate networks.
To mitigate these risks, immediate action is required by all users and administrators managing Firefox installations. The vulnerabilities have been addressed in subsequent updates, specifically Firefox version 154, Firefox ESR 140.14, and Firefox ESR 153.1. Organizations should enforce automated update policies to ensure that all endpoints are patched promptly upon the release of these security fixes. Additionally, implementing application whitelisting or restricting script execution in untrusted zones can provide an additional layer of defense against exploitation attempts while updates propagate across the infrastructure.
From a classification standpoint, these vulnerabilities map closely to Common Weakness Enumeration categories such as CWE-120 Buffer Copy without Checking Size of Input and CWE-416 Use After Free, which are standard descriptors for memory corruption issues in C++ based applications like Firefox. In terms of tactical behavior within the MITRE ATT&CK framework, successful exploitation would facilitate Initial Access via Trusted Software or System Information Discovery if the attacker gains a foothold on the system. The fix emphasizes the importance of maintaining up-to-date software versions to close gaps that could otherwise be exploited by threat actors seeking entry points into secure environments.