CVE-2026-74990 in Firefox
Summary
by MITRE • 08/18/2026
Internally found bugs present in Firefox ESR 115.38, 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 115.39, Firefox ESR 140.14, and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
The reported security issue pertains to a collection of internal bugs identified within specific versions of the Mozilla Firefox web browser, including Firefox Extended Support Release (ESR) versions 115.38, 140.13, and 153.0, as well as the standard release version 153. These vulnerabilities were characterized by evidence of memory corruption or other security-relevant defects that pose a significant risk to system integrity and user data confidentiality. The presence of such flaws indicates potential weaknesses in how the browser handles certain inputs or processes internal state, which could allow an attacker to manipulate program execution flow or access unauthorized memory regions. Although no public exploit code was immediately available at the time of disclosure, security analysts presume that with sufficient effort and resources, these defects could be leveraged for remote code execution or other malicious activities against targeted users.
Memory corruption vulnerabilities are among the most critical classes of software flaws because they can lead to arbitrary code execution when an attacker successfully crafts a payload that triggers the defect. In the context of web browsers like Firefox, such issues often arise from complex interactions between JavaScript engines, rendering components, and native C++ code. The specific nature of these defects suggests potential violations of memory safety principles, which aligns with Common Weakness Enumeration (CWE) categories such as CWE-120 Buffer Copy without Checking Size of Input or CWE-787 Out-of-bounds Write. These weaknesses allow attackers to overwrite adjacent memory structures, potentially gaining control over critical program pointers or data values. The risk is exacerbated by the fact that browsers operate with elevated privileges relative to web content and frequently process untrusted input from remote websites, making them prime targets for drive-by download attacks or malicious script injection.
The operational impact of these vulnerabilities extends beyond individual user compromise to broader organizational security postures if deployed in enterprise environments using ESR versions. An exploited vulnerability could enable an attacker to bypass browser sandboxing mechanisms, which are designed to isolate web content from the underlying operating system. This breach of isolation can lead to full system compromise, allowing for data exfiltration, installation of persistent malware, or use of the compromised machine as part of a botnet. Furthermore, such exploits often serve as initial access vectors in advanced persistent threat campaigns, where they are combined with social engineering tactics like phishing emails containing malicious links that direct users to exploit kits designed to trigger these specific browser flaws.
To mitigate these risks, it is imperative for all organizations and individual users running the affected versions of Firefox to upgrade immediately to patched releases. The vulnerabilities were addressed in Firefox 154, as well as ESR versions 115.39, 140.14, and 153.1. These updates contain code changes that correct the underlying memory management errors or input validation flaws responsible for the defects. In addition to applying patches, administrators should enforce automatic update policies within their deployment infrastructure to ensure timely remediation across all endpoints. Security teams should also monitor for indicators of compromise associated with exploit kits targeting these specific browser versions and consider implementing application whitelisting or strict content security policies to limit the impact if a vulnerability is ever successfully exploited in the wild. This proactive approach aligns with ATT&CK techniques related to initial access via spearphishing links and defense evasion through exploitation of trusted software, emphasizing the need for continuous patch management as a primary control measure.