CVE-2021-4140
CRITICALCVSS 10/10EPSS 1.34%
Last modified
CVE-2021-4140 is a critical-severity vulnerability rated 10/10 on the CVSS scale. It was possible to construct specific XSLT markup that would be able to bypass an iframe sandbox. This vulnerability affects Firefox ESR < 91.5, Firefox < 96, and Thunderbird < 91.5.. EPSS estimates a 1.34% chance of exploitation in the next 30 days.
Description
It was possible to construct specific XSLT markup that would be able to bypass an iframe sandbox. This vulnerability affects Firefox ESR < 91.5, Firefox < 96, and Thunderbird < 91.5.
Metrics
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | < 96.0 |
| Mozilla | Firefox Esr | < 91.5 |
| Mozilla | Thunderbird | < 91.5 |
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1746720Exploit, Issue Tracking, Patch, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2022-01/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2022-02/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2022-03/Vendor Advisory
- https://bugzilla.mozilla.org/show_bug.cgi?id=1746720Exploit, Issue Tracking, Patch, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2022-01/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2022-02/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2022-03/Vendor Advisory
Timeline
- Published
- Last Modified
- Status
- Modified
Frequently Asked Questions
What is CVE-2021-4140?
It was possible to construct specific XSLT markup that would be able to bypass an iframe sandbox. This vulnerability affects Firefox ESR < 91.5, Firefox < 96, and Thunderbird < 91.5.
How severe is CVE-2021-4140?
CVE-2021-4140 has a CVSS score of 10/10 (CRITICAL severity). The EPSS model estimates a 1.34% probability of exploitation in the next 30 days.
How do I fix CVE-2021-4140?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.
How Strix Helps
- How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
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Are you affected by CVE-2021-4140?
Run a free Strix scan to check your systems for this vulnerability.
Scan your code nowSource: NVD / NIST