Cyber Resilience

CVE-2026-2634

Mozilla Firefox ≤ 147.4

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 0.0031 23th percentile
Risk Priority 70 floored blend · peak EPSS

Summary

CVE-2026-2634 is a critical-severity User Interface (UI) Misrepresentation of Critical Information (CWE-451) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Phishing (T1566); ranked at the 23th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

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-2026-2634 is a critical vulnerability in Firefox for iOS that allows malicious scripts to cause desynchronization between the address bar and web content before a server response is received. This enables attacker-controlled pages to be presented under spoofed domains, facilitating UI spoofing. The issue affects Firefox for iOS versions prior to 147.4 and is associated with CWE-451 (User Interface Misrepresentation of Critical Information), with 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).

Any remote attacker can exploit this vulnerability without privileges or user interaction by hosting malicious scripts on a webpage. Successful exploitation tricks users into believing they are visiting a legitimate domain while displaying attacker-controlled content, potentially leading to phishing, credential theft, or other social engineering attacks with high confidentiality, integrity, and availability impacts.

Mozilla fixed this vulnerability in Firefox for iOS 147.4, as detailed in their security advisory (MFSA 2026-12) and Bugzilla entry 1975529. Security practitioners should ensure users update to the patched version to mitigate the risk.

OWASP Top 10 for Web (2025)

A06:2025 Insecure Design

EU & UK References

Vulnerability Data

Malicious scripts could cause desynchronization between the address bar and web content before a response is received in Firefox iOS, allowing attacker-controlled pages to be presented under spoofed domains. This vulnerability was fixed in Firefox for iOS 147.4.

CWE(s)
NVD-CWE-noinfoCWE-451

Related Threats

MITRE ATT&CK Enterprise Techniques

T1566 Phishing Initial Access
Adversaries may send phishing messages to gain access to victim systems.
attack.mitre.org →
T1566.002 Spearphishing Link Initial Access
Adversaries may send spearphishing emails with a malicious link in an attempt to gain access to victim systems.
attack.mitre.org →
T1566.003 Spearphishing via Service Initial Access
Adversaries may send spearphishing messages via third-party services in an attempt to gain access to victim systems.
attack.mitre.org →
T1598 Phishing for Information Reconnaissance
Adversaries may send phishing messages to elicit sensitive information that can be used during targeting.
attack.mitre.org →
T1598.003 Spearphishing Link Reconnaissance
Adversaries may send spearphishing messages with a malicious link to elicit sensitive information that can be used during targeting.
attack.mitre.org →
T1534 Internal Spearphishing Lateral Movement
After they already have access to accounts or systems within the environment, adversaries may use internal spearphishing to gain access to additional information or compromise other users within the same organization.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2025-9183Same product: Mozilla Firefox
CVE-2026-2032Same product: Mozilla Firefox
CVE-2026-13356Same product: Mozilla Firefox
CVE-2026-9078Same product: Mozilla Firefox
CVE-2025-9186Same product: Mozilla Firefox
CVE-2025-14744Same product: Mozilla Firefox
CVE-2024-38313Same product: Mozilla Firefox
CVE-2024-5698Same product: Mozilla Firefox
CVE-2025-8043Same product: Mozilla Firefox
CVE-2026-16403Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 147.4

Mitigating Controls

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.PS-06 mostly match
prevents

Secure SDLC practices directly address design and implementation of accurate, non-spoofable UI elements.

PR.AT-01 partial match
prevents

User awareness training helps people recognize and avoid harm from UI misrepresentation such as phishing, but does not prevent the flaw itself.

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.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect UI misrepresentation vulnerabilities before deployment.

A.6.3 Information security awareness, education and training partial match
prevents

Security awareness training can teach users to recognize UI misrepresentation and phishing attempts.

A.8.23 Web filtering partial match
mitigates

Web filtering can block known phishing sites that exploit UI misrepresentation.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle includes UI/UX security requirements that can prevent misrepresentation of critical information.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate proper display and validation of critical information in the UI.

A.8.28 Secure coding partial match
prevents

Secure coding practices can prevent UI flaws that obscure or spoof critical information.

References