Cyber Posture

CVE-2026-2791

Critical

Published: 24 February 2026

Published
24 February 2026
Modified
13 April 2026
KEV Added
—
Patch
—
CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0003 8.0th percentile
Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Description

Mitigation bypass in the Networking: Cache component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match
prevent

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.

RA-5 Vulnerability Monitoring and Scanning good match
detect

Requires vulnerability scanning to identify systems running vulnerable Firefox or Thunderbird versions affected by CVE-2026-2791, enabling proactive patching.

SI-5 Security Alerts, Advisories, and Directives good match
prevent

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.

Security SummaryAI

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.

Details

CWE(s)
NVD-CWE-noinfoCWE-288

Affected Products

mozilla
firefox
≤ 140.8.0 · ≤ 148.0
mozilla
thunderbird
≤ 140.8.0 · ≤ 148.0

MITRE ATT&CK Enterprise TechniquesAI

T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1562.001 Disable or Modify Tools Stealth
Adversaries may modify and/or disable security tools to avoid possible detection of their malware/tools and activities.
attack.mitre.org →
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).

Confidence: MEDIUM · MITRE ATT&CK Enterprise v18.1

References