Cyber Resilience

CVE-2026-4728

Auth Bypass in Mozilla Firefox ≤ 149.0

Auth Bypass
Published
24 March 2026
Modified
13 April 2026
Patch / advisory
View advisory
CVSS Score v3.1 6.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
EPSS Score 0.0024 15th percentile
Risk Priority 49 floored blend · peak EPSS

Summary

CVE-2026-4728 is a medium-severity Authentication Bypass by Spoofing (CWE-290) vulnerability in Mozilla Firefox. Its CVSS base score is 6.5 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Adversary-in-the-Middle (T1557); ranked at the 15th 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 IA-2 (Identification and Authentication (Organizational Users)) and IA-3 (Device Identification and Authentication) — 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-2026-4728 is a spoofing vulnerability (CWE-290) in the Privacy: Anti-Tracking component of Mozilla Firefox and Thunderbird. The issue allows attackers to bypass authentication mechanisms through spoofing, earning a CVSS v3.1 base score of 6.5 (AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N), classified as medium severity. It was addressed in Firefox version 149 and Thunderbird version 149.

The vulnerability can be exploited by unauthenticated remote attackers over the network with low complexity, but requires user interaction to succeed. Successful exploitation results in high integrity impact, enabling attackers to spoof anti-tracking protections without affecting confidentiality or availability.

Mozilla's security advisories (MFSA 2026-20 and MFSA 2026-23) detail the fix, recommending immediate upgrade to Firefox 149 or Thunderbird 149. Additional technical details are available in Bugzilla entry 2013179.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

Spoofing issue in the Privacy: Anti-Tracking component. This vulnerability was fixed in Firefox 149 and Thunderbird 149.

CWE(s)
CWE-290

Related Threats

MITRE ATT&CK Enterprise Techniques

T1557 Adversary-in-the-Middle Credential Access
Adversaries may attempt to position themselves between two or more networked devices using an adversary-in-the-middle (AiTM) technique to support follow-on behaviors such as [Network Sniffing](https://attack.
attack.mitre.org →
T1557.001 Name Resolution Poisoning and SMB Relay Credential Access
By responding to LLMNR/NBT-NS/mDNS network traffic, adversaries may spoof an authoritative source for name resolution to force communication with an adversary controlled system.
attack.mitre.org →
T1036 Masquerading Stealth
Adversaries may attempt to manipulate features of their artifacts to make them appear legitimate or benign to users and/or security tools.
attack.mitre.org →
T1036.001 Invalid Code Signature Stealth
Adversaries may attempt to mimic features of valid code signatures to increase the chance of deceiving a user, analyst, or tool.
attack.mitre.org →
T1134 Access Token Manipulation Stealth
Adversaries may modify access tokens to operate under a different user or system security context to perform actions and bypass access controls.
attack.mitre.org →
T1134.001 Token Impersonation/Theft Stealth
Adversaries may duplicate then impersonate another user's existing token to escalate privileges and bypass access controls.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-11701Same product: Mozilla Firefox
CVE-2026-8963Same product: Mozilla Firefox
CVE-2026-2800Same product: Mozilla Firefox
CVE-2024-11692Same product: Mozilla Firefox
CVE-2024-10465Same product: Mozilla Firefox
CVE-2026-8960Same product: Mozilla Firefox
CVE-2026-0890Same product: Mozilla Firefox
CVE-2026-6762Same product: Mozilla Firefox
CVE-2026-8961Same product: Mozilla Firefox
CVE-2025-14327Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 149.0
mozilla
thunderbird
≤ 149.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 3 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V6.4.3
  • V10.4.16
  • V10.5.1
  • V11.4.3

Mitigating Controls (NIST 800-53 r5) AI

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

Proper unique identification and authentication of users directly stops spoofing-based bypass of authentication.

IA-3 Device Identification and Authentication good match

Device identification and authentication before connection prevents spoofing of devices to bypass auth.

IA-8 Identification and Authentication (Non-organizational Users) good match

Authentication of non-organizational users blocks external spoofing attempts against the scheme.

IA-5 Authenticator Management good match

Authenticator management ensures credentials cannot be easily spoofed or reused to bypass authentication.

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-04 full match
prevents

Protecting, conveying, and verifying identity assertions specifically prevents the spoofing that enables authentication bypass.

PR.AA-03 mostly match
prevents

Requiring authentication of users/services/hardware directly counters spoofing-based bypass when strong methods are used.

PR.AA-02 partial match
prevents

Proofing and binding identities reduces spoofing opportunities during enrollment but does not address runtime authentication implementation flaws.

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.8.5 Secure authentication full match
degrades

Secure authentication control directly mitigates authentication bypass by spoofing.

A.5.17 Authentication information mostly match
degrades

Authentication information management directly addresses credential handling that prevents spoofing.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect spoofing vulnerabilities but does not prevent them by itself.

A.5.15 Access control partial match
prevents

Access control policy reduces spoofing opportunities but does not prescribe authentication mechanisms.

A.5.16 Identity management partial match
prevents

Identity management supports unique identities but does not guarantee resistance to spoofing.

A.5.18 Access rights partial match
prevents

Access rights assignment limits exposure but does not enforce authentication strength.

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` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (1 rule)
  • V-248827 OL 8 must not have the rsh-server package installed. prevents CWE-290
RHEL 7 (1 rule)
  • V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. prevents CWE-290
RHEL 8 (1 rule)
  • V-230492 RHEL 8 must not have the rsh-server package installed. prevents CWE-290

References