CVE-2021-38503 - CVE House
Back to Database
Status published Critical CVE-2021-38503

The iframe sandbox rules were not correctly applied to XSLT...

Vulnerability Description

The iframe sandbox rules were not correctly applied to XSLT stylesheets, allowing an iframe to bypass restrictions such as executing scripts or navigating the top-level frame. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

Impact Analysis

Refer to official advisory for detailed impact metrics.

Remediation

Ensure systems are updated to the latest vendor-supplied patch levels.

THREAT MONITOR

Am I Vulnerable?

Launch our assessment wizard to check if your infrastructure is exposed to • CVE-2021-38503

Credits & Attribution

No credits recorded in the NVD database.

References

More from Mozilla

View All →
CVE-2025-9187
Memory safety bugs fixed in Firefox 142 and Thunderbird 142
Unknown 0
CVE-2025-9186
Spoofing issue in the Address Bar component of Firefox Focus for Android
Unknown 0
CVE-2025-9185
Memory safety bugs fixed in Firefox ESR 115.27, Firefox ESR 128.14, Thunderbird ESR 128.14, Firefox ESR 140.2, Thunderbird ESR 140.2, Firefox 142 and Thunderbird 142
Unknown 0
CVE-2025-9184
Memory safety bugs fixed in Firefox ESR 140.2, Thunderbird ESR 140.2, Firefox 142 and Thunderbird 142
Unknown 0
CVE-2025-9183
Spoofing issue in the Address Bar component
Unknown 0

Affected Vendor

Affected Software

Firefox, Thunderbird, Firefox ESR
Vulnerable Versions:
unspecified

Timeline

Official Publish: December 8th, 2021
Last Modified: August 4th, 2024
Added to House: July 21st, 2026

CVSS Vectors

V3: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Weaknesses (CWE)

No CWE data available

MITRE ATT&CK TTPs

No associated TTPs found for this vulnerability.