Cyber Resilience

CVE-2026-8948

XSS in Mozilla Firefox ≤ 151.0.0

XSS
Published
19 May 2026
Modified
15 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 9.1
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:N
EPSS Score 0.0042 35th percentile
Risk Priority 67 floored blend · peak EPSS

Summary

CVE-2026-8948 is a critical-severity Permissive Cross-domain Security Policy with Untrusted Domains (CWE-942) vulnerability in Mozilla Firefox. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Browser Session Hijacking (T1185); ranked at the 35th 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-4 (Information Flow Enforcement) and SA-11 (Developer Testing and Evaluation) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A02:2025 Security MisconfigurationA05:2025 Injection

EU & UK References

Vulnerability Data

Same-origin policy bypass in the DOM: Networking component. This vulnerability was fixed in Firefox 151 and Thunderbird 151.

CWE(s)
CWE-942CWE-79

Related Threats

MITRE ATT&CK Enterprise Techniques

T1185 Browser Session Hijacking Collection
Adversaries may take advantage of security vulnerabilities and inherent functionality in browser software to change content, modify user-behaviors, and intercept information as part of various browser session hijacking techniques.
attack.mitre.org →
T1539 Steal Web Session Cookie Credential Access
An adversary may steal web application or service session cookies and use them to gain access to web applications or Internet services as an authenticated user without needing credentials.
attack.mitre.org →
T1659 Content Injection Initial Access
Adversaries may gain access and continuously communicate with victims by injecting malicious content into systems through online network traffic.
attack.mitre.org →
T1189 Drive-by Compromise Initial Access
Adversaries may gain access to a system through a user visiting a website over the normal course of browsing.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
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 →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-5758Same product: Mozilla Firefox
CVE-2023-42808Same vendor: Mozilla
CVE-2023-5496Same product: Mozilla Firefox
CVE-2023-25837Shared CWE-79
CVE-2023-22438Shared CWE-79
CVE-2023-27614Shared CWE-79
CVE-2023-47164Shared CWE-79
CVE-2023-49145Shared CWE-79
CVE-2023-47853Shared CWE-79
CVE-2023-28474Shared CWE-79

Affected Assets

mozilla
firefox
≤ 151.0.0
mozilla
thunderbird
≤ 151.0.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V3.4.3
  • V3.4.6
  • V1.1.2
  • V1.3.2

Mitigating Controls (NIST 800-53 r5) AI

AC-4 Information Flow Enforcement good match

Information flow enforcement requires approved authorizations and would reject policies permitting untrusted domains.

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover missing or incorrect input neutralization through targeted web-application tests.

SI-10 Information Input Validation good match

Input validation directly enforces neutralization of untrusted data before it reaches web output generation.

SI-15 Information Output Filtering good match

Output filtering can catch or sanitize unneutralized script content before it is served to users.

SC-7 Boundary Protection partial match

Boundary protection at external interfaces stops unauthorized cross-domain communication allowed by permissive policies.

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-01 mostly match
prevents

Hardened configuration baselines and reviews directly prevent permissive CSP or cross-domain policies.

PR.PS-06 mostly match
prevents

Secure SDLC activities include review and testing of web security policies to avoid untrusted domains.

ID.RA-01 partial match
prevents

Vulnerability identification processes can surface permissive policy misconfigurations.

PR.PS-02 partial match
prevents

Patching and EOL replacement can remediate known XSS instances in libraries or frameworks (partial) but do nothing to enforce input neutralization in application code (none).

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 overly permissive cross-domain policies but does not prevent their initial introduction.

A.5.6 Contact with special interest groups partial match
prevents

Knowledge exchange on emerging attack techniques and patches reduces the likelihood that cross-site scripting flaws remain unaddressed in deployed applications.

A.5.7 Threat intelligence partial match
prevents

Operational indicators of compromise for web-application attacks can be incorporated into WAF or input-filtering rules, lowering the likelihood that unsanitized data reaches the browser.

A.8.20 Networks security partial match
degrades

Network security policies can restrict cross-domain communication but do not specifically mandate strict CSP or cross-domain policy configuration.

A.8.21 Security of network services partial match
degrades

Security of network services includes defining allowed endpoints, which can limit untrusted domains but does not directly address web-client policy files.

A.8.23 Web filtering partial match
degrades

Web filtering can block untrusted domains at the network level, partially mitigating permissive cross-domain policies.

References