Security Resilience

CVE-2026-2791

Auth Bypass in Mozilla Firefox ≤ 140.8.0

Auth Bypass
Published
24 February 2026
Modified
13 April 2026
Patch / advisory
View advisory
CVSS Score v3.1 9.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0055 45th percentile
Risk Priority 72 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

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 Data Obfuscation (T1001); ranked at the 45th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to AC-25 (Reference Monitor) and AC-3 (Access Enforcement) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

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)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

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)
NVD-CWE-noinfoCWE-288

Related Threats

MITRE ATT&CK Enterprise Techniques

T1001 Data Obfuscation Command And Control
Adversaries may obfuscate command and control traffic to make it more difficult to detect.
attack.mitre.org →
T1003.001 LSASS Memory Credential Access
Adversaries may attempt to access credential material stored in the process memory of the Local Security Authority Subsystem Service (LSASS).
attack.mitre.org →
T1003.002 Security Account Manager Credential Access
Adversaries may attempt to extract credential material from the Security Account Manager (SAM) database either through in-memory techniques or through the Windows Registry where the SAM database is stored.
attack.mitre.org →
T1018 Remote System Discovery Discovery
Adversaries may attempt to get a listing of other systems by IP address, hostname, or other logical identifier on a network that may be used for Lateral Movement from the current system.
attack.mitre.org →
T1027.006 HTML Smuggling Stealth
Adversaries may smuggle data and files past content filters by hiding malicious payloads inside of seemingly benign HTML files.
attack.mitre.org →
T1027.009 Embedded Payloads Stealth
Adversaries may embed payloads within other files to conceal malicious content from defenses.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-2784Same product: Mozilla Firefox
CVE-2026-6768Same product: Mozilla Firefox
CVE-2026-6760Same product: Mozilla Firefox
CVE-2026-2775Same product: Mozilla Firefox
CVE-2025-10531Same product: Mozilla Firefox
CVE-2026-6771Same product: Mozilla Firefox
CVE-2025-13013Same product: Mozilla Firefox
CVE-2025-3932Same product: Mozilla Thunderbird
CVE-2025-13018Same product: Mozilla Firefox
CVE-2026-12298Same product: Mozilla Firefox

Affected Assets

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

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 7 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V6.4.3
  • V6.6.1
  • V12.1.3

Mitigating Controls (NIST 800-53 r5) AI

AC-25 Reference Monitor good match

Requires a tamperproof, always-invoked reference monitor that structurally blocks bypass via any alternate path.

AC-3 Access Enforcement good match

Enforces authorization checks on every logical access path, eliminating unauthenticated alternate channels.

IA-2 Identification and Authentication (Organizational Users) good match

Mandates unique identification and authentication for all organizational users, covering the primary authentication requirement.

SC-7 Boundary Protection partial match

Controls all external and key internal interfaces, reducing the chance of unauthenticated alternate channels.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-03 partial match
blocks

Requiring authentication on every channel and path directly eliminates alternate-path bypasses.

PR.AA-05 partial match
blocks

Enforcing authorizations and least privilege across all access vectors prevents unauthenticated alternate paths.

PR.IR-01 partial match
blocks

Protecting networks and environments from unauthorized logical access blocks bypass via undocumented channels.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.14 Information transfer partial match
removes
A.5.15 Access control partial match
blocks

A.5.15 only requires defining a topic-specific access control policy and determining requirements; it does not itself enforce, implement or configure any access rules that would stop an alternate unauthenticated path from being exploitable.

A.5.16 Identity management partial match
removes
A.5.17 Authentication information partial match
removes
A.5.18 Access rights partial match
blocks

Access rights provisioning and review prevent bypass via unmonitored or alternate channels.

A.8.10 Information deletion partial match
removes

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (higher-evidence rows only; rows rated `none` are excluded).

Oracle Linux 8 (2 rules)
  • V-248598 There must be no ".shosts" files on the OL 8 operating system. blocks CWE-288
  • V-248827 OL 8 must not have the rsh-server package installed. blocks CWE-288
Oracle Linux 9 (2 rules)
  • V-271757 OL 9 file systems must not contain shosts.equiv files. blocks CWE-288
  • V-271758 OL 9 file systems must not contain .shosts files. blocks CWE-288
RHEL 7 (3 rules)
  • 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. blocks CWE-288
  • V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. blocks CWE-288
  • V-204424 The Red Hat Enterprise Linux operating system must not allow accounts configured with blank or null passwords. blocks CWE-288

References