CVE-2026-2791 is a security vulnerability identified in the Networking: Cache component of Mozilla Firefox, affecting versions prior to 148 and Firefox ESR versions prior to 140.8. The vulnerability is classified as a mitigation bypass, meaning it allows attackers to circumvent existing security controls designed to protect cached network data. The cache component in browsers stores web content to improve performance and reduce bandwidth usage; however, improper handling or bypassing of mitigations in this component can lead to unauthorized access to sensitive cached data or facilitate other attacks such as cache poisoning or information disclosure. Although specific technical details such as the exact nature of the bypass or the underlying cause are not provided, mitigation bypass vulnerabilities typically exploit flaws in how security boundaries are enforced within the caching mechanism. No CVSS score has been assigned yet, and no known exploits are reported in the wild, indicating that the vulnerability is newly disclosed and may not yet be actively exploited. The flaw affects both the standard Firefox release and the Extended Support Release (ESR), which is widely used in enterprise environments for stability and long-term support. Given Firefox's broad user base across desktop and mobile platforms, this vulnerability has the potential to impact a large number of users globally. The vulnerability was reserved and published in February 2026, with Mozilla as the assigner, but no official patches or detailed technical advisories are currently linked, suggesting that fixes may be forthcoming or in development.

The potential impact of CVE-2026-2791 is significant due to the widespread use of Mozilla Firefox as a primary web browser for both individual users and organizations. A mitigation bypass in the caching component can lead to unauthorized access to sensitive cached data, which may include authentication tokens, personal information, or other confidential content retrieved during web sessions. This could result in privacy breaches, session hijacking, or facilitate further exploitation such as cross-site scripting (XSS) or man-in-the-middle attacks if attackers manipulate cached content. For organizations, especially those with strict data protection requirements, this vulnerability could undermine confidentiality and integrity of web communications. The absence of known exploits reduces immediate risk, but the ease of exploitation is potentially high if the vulnerability can be triggered remotely without authentication or user interaction, as is common with browser-based flaws. The scope is broad given Firefox's global market penetration, affecting both consumer and enterprise users. Disruption of availability is less likely but cannot be ruled out if the vulnerability is leveraged to cause cache corruption or browser crashes. Enterprises relying on Firefox ESR for stability may face delayed patching cycles, increasing exposure duration. Overall, the vulnerability poses a medium to high risk until mitigated.

Organizations and users should prepare to update Mozilla Firefox to version 148 or later, and Firefox ESR to version 140.8 or later, as soon as these patches are officially released by Mozilla. Until patches are available, consider the following specific mitigations: 1) Implement network-level protections such as web filtering and intrusion detection systems to monitor and block suspicious traffic targeting Firefox clients. 2) Educate users about the risks of visiting untrusted websites that may attempt to exploit browser vulnerabilities. 3) For enterprise environments, consider temporarily restricting Firefox usage or deploying alternative browsers with no known vulnerabilities if critical operations are at risk. 4) Enable strict cache control headers on internal web applications to minimize sensitive data caching. 5) Monitor Mozilla security advisories and threat intelligence feeds for updates or exploit reports related to CVE-2026-2791. 6) Employ endpoint detection and response (EDR) solutions to detect anomalous browser behavior indicative of exploitation attempts. 7) Conduct internal vulnerability assessments and penetration testing focusing on browser security to identify potential exposure. These targeted actions go beyond generic patching advice and help reduce risk during the vulnerability window.