Is CVE-2026-9309 in the CISA KEV catalog?

No. CVE-2026-9309 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-9309?

CVE-2026-9309 has a CVSS v3 base score of 5.4 (MEDIUM).

What is the EPSS score for CVE-2026-9309?

CVE-2026-9309 has an EPSS score of 0.16% (5th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-9309?

Upgrade DeveloperEdition to 151.2 or later. Fixes are available for 2 affected products.

CVE & CISA-KEV Catalog

CVE-2026-9309

MEDIUM

5.4

CVSS v3

NVD

Description

Firefox for iOS Reader View did not properly escape HTML tags in JSON-LD metadata. A malicious page could inject markup that changed Reader View behavior and leaked sensitive URL parameters. These parameters could then be used to access internal pages, potentially resulting in arbitrary JavaScript execution in an internal origin. This vulnerability was fixed in Firefox for iOS 151.2.

CWE-79Cross-Site Scripting (XSS)

How to fix

Remediation Available

DeveloperEditionWindows application

Affected:151.2Fixed in:151.2Mozilla

Mozilla Firefox (en-US)Windows application

Affected:151.2Fixed in:151.2Mozilla

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 InteractionRequired

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

0.16%probability of exploitation in 30 days

5thpercentile

Low risk: more likely to be exploited than 5% of all known CVEs.

References

Vendor Advisory1

mozilla.org

Other references1

bugzilla.mozilla.org

Related Vulnerabilities

Other CWE-79 (Cross-Site Scripting (XSS)) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2020-11022	Medium	6.9	99%	-	Fix
CVE-2019-3929	Critical	9.8	99%	KEV	Fix
CVE-2020-9496	Medium	6.1	99%	-	-
CVE-2023-28341	Medium	6.1	99%	-	Fix
CVE-2018-12998	Medium	6.1	98%	-	-
CVE-2025-4123	High	7.6	98%	-	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 2026-06-03.