CVE-2015-7327 in Firefox
Summary
by MITRE
Mozilla Firefox before 41.0 does not properly restrict the availability of High Resolution Time API times, which allows remote attackers to track last-level cache access, and consequently obtain sensitive information, via crafted JavaScript code that makes performance.now calls.
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Analysis
by VulDB Data Team • 06/19/2022
The vulnerability identified as CVE-2015-7327 represents a significant privacy and security flaw in Mozilla Firefox versions prior to 41.0, specifically targeting the High Resolution Time API implementation. This weakness stems from insufficient restrictions on time measurement capabilities that should otherwise be protected from precise tracking by malicious actors. The vulnerability operates through the performance.now() JavaScript method which provides access to high-resolution time measurements with nanosecond precision, creating a potential attack vector for sophisticated tracking mechanisms.
The technical flaw manifests in how Firefox handles the High Resolution Time API, which is designed to provide developers with precise timing information for performance measurement and animation purposes. However, the implementation failed to adequately isolate these timing measurements from potential tracking attacks that could exploit the consistent timing patterns of cache access operations. When attackers craft malicious JavaScript code that repeatedly calls performance.now(), they can observe subtle timing variations that correlate with last-level cache access patterns, effectively creating a side-channel attack vector.
This vulnerability enables remote attackers to perform cache-based tracking that can reveal sensitive information about user behavior and system state. The attack exploits the fact that cache access times vary predictably based on whether data is present in the cache, allowing attackers to infer information about recently accessed resources. The precision of the High Resolution Time API, combined with the consistent nature of cache access timing, creates a fingerprinting capability that can be used to track users across different websites and sessions, compromising user privacy and potentially exposing confidential browsing patterns.
The operational impact of this vulnerability extends beyond simple tracking, as it enables sophisticated surveillance capabilities that can be used to reconstruct user activity patterns and potentially identify sensitive information. The attack can be particularly effective in environments where cache timing variations correlate with access to personal data, financial records, or other confidential resources. This vulnerability aligns with CWE-203, which addresses the exposure of sensitive information through side-channel timing attacks, and represents a significant concern for privacy-focused applications and environments where user confidentiality is paramount.
Security professionals should note that this vulnerability operates under ATT&CK technique T1070.004, which involves the use of system information discovery to gather intelligence about the target environment. The vulnerability's exploitation demonstrates how seemingly benign API implementations can be weaponized for surveillance purposes, requiring careful monitoring of timing-based tracking patterns in web applications. Organizations should implement immediate mitigations including Firefox updates to version 41.0 or later, along with monitoring for suspicious timing-based JavaScript behavior that could indicate exploitation attempts.
The remediation strategy involves updating Firefox installations to versions that properly restrict access to high-resolution timing information and implement appropriate sandboxing for timing APIs. Browser vendors should ensure that timing APIs are adequately protected from side-channel attacks while maintaining functionality for legitimate development purposes. Additional mitigations include implementing Content Security Policy directives that limit access to performance APIs and monitoring network traffic for unusual timing-based patterns that may indicate tracking attempts. The vulnerability highlights the importance of considering side-channel attack vectors during API design and implementation phases, emphasizing the need for comprehensive security testing that includes timing-based attack scenarios.