CVE-2026-9309: Firefox for iOS Reader View did not properly escape HTML tags in JSON-LD metadata

Q: How do I fix CVE-2026-9309?

firefox: upgrade to 151.2. Exact commands for each OS are on this page.

Q: Is CVE-2026-9309 being exploited?

CVE-2026-9309 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-9309 affect?

CVE-2026-9309 affects firefox. Severity is medium (CVSS 5.4). 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 int

Q: How urgent is CVE-2026-9309?

Priority 20/100. No elevated risk signals yet.

Routine

MEDIUM 5.4UPGRADE

CVE-2026-9309 is a medium-severity flaw (CVSS 5.4) affecting firefox. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 95%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-06-01
Last modified	2026-07-22

Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Last updated 2026-07-22 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-01 13:16 UTCPublished CVE record published
2026-07-22 07:10 UTCUpdated Record last modified

mozilla firefox UPGRADE

Affected: < 151.2

Fixed in: 151.2

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy firefox || rpm -q firefox || firefox --version

2. UPGRADE to 151.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade firefox

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade firefox

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-9309?

firefox: upgrade to 151.2. Exact commands for each OS are on this page.

Is CVE-2026-9309 being exploited?

CVE-2026-9309 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-9309 affect?

CVE-2026-9309 affects firefox. Severity is medium (CVSS 5.4). 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 int

How urgent is CVE-2026-9309?

Priority 20/100. No elevated risk signals yet.

Software pages

iOS vulnerabilities · Mozilla Firefox vulnerabilities

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References

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