CVE-2026-74954 in Firefox
Summary
by MITRE • 08/18/2026
Information disclosure due to side-channel in the Storage: Cache API component. This vulnerability was fixed in Firefox 154 and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
The identified vulnerability represents a critical information leakage vector within the Mozilla Firefox browser, specifically targeting the Storage Cache Application Programming Interface. As a side-channel attack, this flaw does not rely on traditional logical errors or buffer overflows but instead exploits timing differences in how the system processes cache operations. By measuring the time required for specific storage-related API calls to complete, an attacker can infer sensitive data about the state of the browser's internal caching mechanisms. This type of vulnerability is particularly insidious because it bypasses standard sandboxing and permission models that typically prevent direct access to private user data or cross-origin resources. The core technical flaw lies in the lack of constant-time execution for certain cache retrieval and validation operations, allowing external scripts running within a webpage to deduce whether specific cached entries exist based on subtle variations in response latency.
From an operational perspective, this vulnerability enables sophisticated tracking and fingerprinting attacks that compromise user privacy at a granular level. Attackers can leverage the side-channel to determine which resources have been previously visited by the user or to identify active sessions across different tabs or windows. This capability effectively neutralizes many of the privacy protections offered by modern browsers, such as private browsing modes or strict cookie policies, because the cache state remains accessible through timing analysis even when other data channels are restricted. The impact extends beyond simple tracking; in enterprise environments where sensitive documents might be cached locally for performance optimization, this flaw could potentially allow malicious scripts to detect the presence of specific internal resources, thereby aiding in targeted phishing campaigns or corporate espionage efforts by confirming the existence of particular web applications or services used within an organization.
The remediation strategy implemented in Firefox version 154 and Firefox Extended Support Release (ESR) version 153.1 addresses this issue by enforcing constant-time execution patterns for cache API operations. This involves modifying the underlying code to ensure that processing time does not vary based on whether a cache entry exists or what its content is, thereby eliminating the timing signal available to attackers. Additionally, developers have likely introduced stricter isolation boundaries between different origin contexts accessing the storage subsystem to prevent cross-origin side-channel exploitation. For system administrators and end-users, it is imperative to update immediately to these patched versions to mitigate the risk of privacy erosion. Organizations should also consider implementing Content Security Policy directives that restrict access to certain APIs if they are not strictly necessary for their web applications, thereby reducing the attack surface even further in case similar vulnerabilities arise in future releases.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-208, which describes observable timing discrepancy, and is closely related to CWE-359 regarding exposure of private information through side channels. In terms of threat modeling, this attack vector corresponds to the ATT&CK technique T1564.007, known as Hidden Window, although more accurately it falls under data exfiltration via side-channel timing analysis rather than window manipulation. The exploitation typically requires a malicious webpage or script with access to the DOM and the ability to make precise time measurements using high-resolution timers available in modern JavaScript environments. While the browser's sandbox prevents direct memory reads, the temporal leakage provides an indirect path to sensitive state information. Security teams should monitor for any attempts to abuse timing APIs within their web applications and ensure that all client-side software is kept up to date with the latest security patches provided by Mozilla to maintain robust defense-in-depth against such subtle but effective privacy violations.