CVE-2026-16391 in Firefox
Summary
by MITRE • 07/21/2026
Information disclosure in the Storage: IndexedDB component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13.
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Analysis
by VulDB Data Team • 07/21/2026
This information disclosure vulnerability resides within the Storage: IndexedDB component of Mozilla Firefox, representing a critical security flaw that could potentially expose sensitive user data through improper access controls or inadequate data isolation mechanisms. The vulnerability affects both regular Firefox releases and the Extended Support Release version, indicating its widespread impact across different deployment scenarios. IndexedDB serves as a client-side storage mechanism that allows web applications to store significant amounts of structured data locally within browsers, making it a prime target for exploitation by malicious actors seeking to access user information.
The technical nature of this flaw suggests that unauthorized parties may have gained access to data stored in IndexedDB databases without proper authorization or authentication mechanisms. This could occur through various attack vectors including cross-site scripting exploits, privilege escalation techniques, or other browser-based vulnerabilities that allow attackers to bypass normal security boundaries. The vulnerability likely stems from insufficient validation of access permissions or inadequate sandboxing of IndexedDB operations, potentially allowing malicious websites to read data from other origins or accessing internal browser storage mechanisms.
From an operational perspective, this information disclosure vulnerability poses significant risks to user privacy and data protection. Attackers could potentially extract personal information, session tokens, authentication credentials, or other sensitive data stored in IndexedDB databases across different web applications. The impact extends beyond individual user privacy concerns to encompass potential corporate data breaches when users access business applications through vulnerable browsers. Organizations relying on Firefox for enterprise deployments face increased risk of data leakage and compliance violations when this vulnerability remains unpatched.
The fix implemented in Firefox version 153 and Firefox ESR 140.13 addresses the underlying security flaw through enhanced access controls and improved isolation mechanisms within the IndexedDB component. Security patches typically involve strengthening the security model that governs how different origins can access storage resources, implementing stricter validation of cross-origin requests, or modifying the internal architecture to prevent unauthorized data access patterns. This remediation aligns with industry best practices for secure browser implementation and follows established security frameworks such as those defined in the CWE (Common Weakness Enumeration) catalog under weakness categories related to information exposure and privilege escalation.
Organizations should prioritize immediate deployment of these security updates across all Firefox installations to mitigate potential exploitation risks. Security teams should conduct thorough vulnerability assessments to identify any systems that may still be running vulnerable versions, particularly in enterprise environments where browser updates might be delayed or restricted. The mitigation strategy should include monitoring for potential exploitation attempts through network traffic analysis and implementing additional defensive measures such as web application firewalls to detect unusual access patterns targeting IndexedDB storage mechanisms.
This vulnerability demonstrates the ongoing challenges in securing modern web browsers where complex storage systems must balance functionality with security requirements. It highlights the importance of continuous security testing and the need for robust threat modeling when designing browser components that handle sensitive user data. The remediation process should be viewed as part of a broader security posture improvement initiative, incorporating regular security assessments, penetration testing, and adherence to secure coding practices throughout the software development lifecycle. Organizations should also consider implementing additional monitoring solutions specifically designed to detect unauthorized access attempts to client-side storage mechanisms as part of their overall cybersecurity defense strategy.
Reference to relevant ATT&CK techniques shows this vulnerability could map to T1531 (Account Access Removal) or T1070 (Indicator Removal on Host) when exploited, though primarily it represents a data exposure issue that could lead to broader compromise scenarios through information gathering phases of attack chains. The fix addresses fundamental security architecture issues within the browser's storage subsystem and aligns with security standards such as those outlined in NIST SP 800-53 for secure system design and implementation practices.