CVE-2026-2791
Published: 24 February 2026
Summary
CVE-2026-2791 is a critical-severity Authentication Bypass Using an Alternate Path or Channel (CWE-288) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked at the 32.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 RA-5 (Vulnerability Monitoring and Scanning) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-2791 is a mitigation bypass vulnerability in the Networking: Cache component of Mozilla Firefox and Thunderbird. The issue, published on 2026-02-24, affects versions prior to Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8, where it was fixed. It is associated with CWE-288 and carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating critical severity.
Remote attackers require no privileges or user interaction to exploit this vulnerability over the network with low attack complexity. Successful exploitation enables high-impact disruption to confidentiality, integrity, and availability, allowing attackers to bypass security mitigations via the cache component.
Mozilla's security advisories (MFSA2026-13, MFSA2026-15, MFSA2026-16, and MFSA2026-17), along with Bugzilla entry 2015220, document the vulnerability and confirm that updating to the specified fixed versions—Firefox 148, Firefox ESR 140.8, Thunderbird 148, or Thunderbird 140.8—mitigates the issue.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8442
Vulnerability details
Mitigation bypass in the Networking: Cache component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Mitigation bypass in browser cache component (CWE-288) with no-auth remote trigger and full CIA impact directly enables client-side exploitation (T1203) while impairing defenses by subverting security controls (T1562.001).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly mandates timely remediation of critical flaws like CVE-2026-2791 through vendor patches to Firefox 148 and Thunderbird 140.8, preventing exploitation of the cache mitigation bypass.
Requires vulnerability scanning to identify systems running vulnerable Firefox or Thunderbird versions affected by CVE-2026-2791, enabling proactive patching.
Ensures monitoring and application of security advisories such as MFSA2026-13 to promptly update browsers and mitigate the cache component bypass in CVE-2026-2791.
Hardening callouts derived
Configuration rules from DISA STIG baselines that reduce the attack surface for weaknesses of the type cited by this CVE. Derived transitively via CVE→CWE→STIG over `controls_xwalks` (authoritative rows only).
Oracle Linux 8 (2 rules)
- V-248598 There must be no ".shosts" files on the OL 8 operating system. via CWE-288
- V-248827 OL 8 must not have the rsh-server package installed. via CWE-288
Oracle Linux 9 (2 rules)
- V-271757 OL 9 file systems must not contain shosts.equiv files. via CWE-288
- V-271758 OL 9 file systems must not contain .shosts files. via CWE-288
RHEL 7 (3 rules)
- V-204424 The Red Hat Enterprise Linux operating system must not allow accounts configured with blank or null passwords. via CWE-288
- V-204440 Red Hat Enterprise Linux operating systems version 7.2 or newer using Unified Extensible Firmware Interface (UEFI) must require authentication upon booting into single-user and maintenance modes. via CWE-288
- V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. via CWE-288