CVE-2026-74957 in Firefox
Summary
by MITRE • 08/18/2026
Mitigation bypass in the Safe Browsing component. 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 • 08/18/2026
The identified security issue represents a critical failure within Mozilla's Safe Browsing subsystem, specifically involving the bypass of mitigation controls designed to protect users from malicious web content. This vulnerability allows an attacker to circumvent the protective mechanisms that typically block access to known phishing sites or malware distribution platforms. The root cause lies in how the browser processes and validates URLs against its threat intelligence lists, suggesting a logic error or insufficient validation step during the lookup process. By exploiting this flaw, an adversary can construct specific URL patterns or request structures that evade detection by the Safe Browsing service while still loading malicious payloads on the client side. This effectively neutralizes one of the primary layers of defense in modern web browsers, leaving end-users exposed to social engineering attacks and automated malware infections without any warning indicators such as red warning pages or blocked content notifications.
From a technical perspective, this flaw likely stems from improper sanitization of input data before it is compared against threat databases or insufficient handling of edge cases in the URL parsing logic. Safe Browsing relies on hashing techniques to efficiently query remote servers for potential threats; if an attacker can manipulate these hashes or exploit race conditions during the asynchronous lookup process, they may successfully bypass the blocklist checks. The vulnerability highlights a gap between the intended security policy and its actual implementation within the browser engine. Such issues are particularly dangerous because they operate silently in the background, allowing malicious scripts to execute before any user-facing intervention can occur. This undermines the trust model of the browser, as users rely on these automated systems to filter out known bad actors without requiring constant manual oversight or technical expertise from the average internet user.
The operational impact of this vulnerability is severe, primarily affecting the confidentiality and integrity of user data. Successful exploitation enables phishing campaigns that appear legitimate because they are not flagged by the browser's built-in protections. Attackers can host credential harvesting pages on domains that should have been blacklisted, leading to unauthorized access to sensitive accounts such as banking services, email providers, or corporate intranets. Furthermore, malware distribution sites become accessible without warning, increasing the risk of drive-by downloads and subsequent system compromise. In enterprise environments where Firefox is deployed via group policy with strict Safe Browsing settings enabled, this bypass renders those configurations ineffective against targeted attacks that leverage known malicious infrastructure. The lack of user notification means victims may interact freely with hostile content, potentially leading to data exfiltration, ransomware deployment, or persistent backdoor installation on affected systems.
To address this risk, immediate action is required by upgrading the Firefox browser ecosystem to version 154 for standard releases and versions 140.14 and 153.1 for Extended Support Release channels. These updates contain the necessary patches that correct the logic errors within the Safe Browsing component, ensuring that URL validation processes properly enforce threat intelligence blocks. Organizations should verify their deployment pipelines to ensure all endpoints are updated promptly. Additionally, administrators can supplement browser-level protections by implementing network-based filtering solutions and enforcing strict Content Security Policies where applicable. Users should remain vigilant for any unusual behavior from websites they visit regularly, although reliance on the patched software is the primary defense against this specific class of vulnerability. Continuous monitoring of Mozilla's security advisories remains essential to stay ahead of emerging threats that may target other components of the browser stack.
This incident aligns with common weakness categories found in web application and client-side security frameworks. It corresponds closely to CWE-20 Improper Input Validation, as the failure originated from inadequate checking of URL inputs against expected safe patterns or threat lists. Furthermore, it relates to CWE-749 Exposed Dangerous Method if the bypass involved invoking internal APIs incorrectly, though input validation is the more likely culprit in Safe Browsing contexts. In terms of offensive security tactics, this vulnerability facilitates techniques associated with MITRE ATT&CK ID T1583 Acquire Infrastructure and T1071 Application Layer Protocol, as attackers use legitimate-looking channels to deliver malicious payloads while evading detection mechanisms designed to identify hostile traffic patterns. Understanding these mappings helps in categorizing the severity and developing more robust defense-in-depth strategies that do not rely solely on single-point mitigations like Safe Browsing but instead incorporate multiple layers of verification and monitoring.