CVE-2026-16403: Spoofing issue in the Address Bar component

Q: How do I fix CVE-2026-16403?

firefox: upgrade to 153.0.0; thunderbird: upgrade to 153.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-16403 being exploited?

CVE-2026-16403 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-2026-16403 affect?

CVE-2026-16403 affects firefox, thunderbird. Severity is medium (CVSS 6.5). Spoofing issue in the Address Bar component. This vulnerability was fixed in Firefox 153 and Thunderbird 153.

Q: How urgent is CVE-2026-16403?

Priority 25/100. No elevated risk signals yet.

Routine

MEDIUM 6.5UPGRADEUPGRADE

CVE-2026-16403 is a medium-severity flaw (CVSS 6.5) affecting firefox, thunderbird. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Spoofing issue in the Address Bar component. This vulnerability was fixed in Firefox 153 and Thunderbird 153.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 91%)
CISA exploited list	No
Weakness	CWE-451
Published	2026-07-21
Last modified	2026-10-24

Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-21 13:17 UTCPublished CVE record published
2026-10-24 20:10 UTCUpdated Record last modified

mozilla firefox UPGRADE

Affected: < 153.0.0

Fixed in: 153.0.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 153.0.0 (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.

mozilla thunderbird UPGRADE

Affected: < 153.0

Fixed in: 153.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 153.0 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade thunderbird

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-2026-16403?

firefox: upgrade to 153.0.0; thunderbird: upgrade to 153.0. Exact commands for each OS are on this page.

Is CVE-2026-16403 being exploited?

CVE-2026-16403 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-2026-16403 affect?

CVE-2026-16403 affects firefox, thunderbird. Severity is medium (CVSS 6.5). Spoofing issue in the Address Bar component. This vulnerability was fixed in Firefox 153 and Thunderbird 153.

How urgent is CVE-2026-16403?

Priority 25/100. No elevated risk signals yet.

Software pages

Mozilla Firefox vulnerabilities · Mozilla Thunderbird vulnerabilities

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References

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