Is CVE-2021-38503 in the CISA KEV catalog?

No. CVE-2021-38503 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-38503?

CVE-2021-38503 has a CVSS v3 base score of 10.0 (CRITICAL).

What is the EPSS score for CVE-2021-38503?

CVE-2021-38503 has an EPSS score of 3.83% (89th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-38503?

Upgrade firefox on debian unstable to 94.0-1 or later. Fixes are available for 7 affected products.

CVE & CISA-KEV Catalog

CVE-2021-38503

CRITICALEPSS 89th pctl

10.0

CVSS v3

NVD

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.

CWE-863Incorrect Authorization

How to fix

Remediation Available

firefoxDebian

Fixed in:94.0-1CVE-2021-38503

firefoxUbuntu

Fixed in:94.0+build3-0ubuntu0.18.04.1USN-5131-1

Fixed in:94.0+build3-0ubuntu0.20.04.1USN-5131-1

thunderbirdUbuntu

Fixed in:1:91.5.0+build1-0ubuntu0.18.04.1USN-5248-1

Fixed in:1:91.5.0+build1-0ubuntu0.20.04.1USN-5248-1

DeveloperEditionWindows application

Affected:94.0Fixed in:94.0Mozilla

Mozilla Firefox (en-US)Windows application

Affected:94.0Fixed in:94.0Mozilla

Mozilla Firefox ESR (en-US)Windows application

Affected:91.3Fixed in:91.3Mozilla

Mozilla Thunderbird (en-US)Windows application

Affected:91.3Fixed in:91.3Mozilla

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeChanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Exploit Intelligence

3.83%probability of exploitation in 30 days

89thpercentile

Elevated risk: more likely to be exploited than 89% of all known CVEs.

References

Vendor Advisory4

Third-Party Advisory6

Related Vulnerabilities

Other CWE-863 (Incorrect Authorization) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-22518	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2023-38035	Critical	9.8	100%	KEV + Ransom	-
CVE-2022-46169	Critical	9.8	100%	KEV	Fix
CVE-2025-29927	Critical	9.1	100%	-	Fix
CVE-2024-38856	Critical	9.8	99%	KEV	Fix
CVE-2020-36289	Medium	5.3	99%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.