CVE-2025-6425: An attacker who enumerated resources from the WebCompat extension could have obtained a persistent UUID that i

Routine

MEDIUM 4.3UPGRADE

CVE-2025-6425 is a medium-severity flaw (CVSS 4.3) affecting firefox. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An attacker who enumerated resources from the WebCompat extension could have obtained a persistent UUID that identified the browser, and persisted between containers and normal/private browsing mode, but not profiles. This vulnerability was fixed in Firefox 140, Firefox ESR 115.25, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 77%)
CISA exploited list	No
Weakness	CWE-200
Published	2025-06-24
Last modified	2026-10-23

Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Am I affected?

Timeline

2025-06-24 13:15 UTCPublished CVE record published
2026-10-23 22:10 UTCUpdated Record last modified

mozilla firefox UPGRADE

Affected: < 115.25.0 · < 140.0 · >= 116.0 and < 128.12.0

Fixed in: 115.25.0, 128.12.0, 140.0

Safe to downgrade to: a release before 116.0

1. Check installed version

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

2. UPGRADE to 115.25.0 (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.

3. If no update is available yet, DOWNGRADE to a release before 116.0 (Debian / Ubuntu)

apt-cache madison firefox sudo apt install firefox=<VERSION_BEFORE_116.0> sudo apt-mark hold firefox

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list firefox sudo dnf downgrade firefox-<VERSION_BEFORE_116.0> sudo dnf versionlock add firefox

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2025-6425?

firefox: upgrade to 115.25.0, 128.12.0, 140.0. Exact commands for each OS are on this page.

Is CVE-2025-6425 being exploited?

CVE-2025-6425 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-2025-6425 affect?

CVE-2025-6425 affects firefox. Severity is medium (CVSS 4.3). An attacker who enumerated resources from the WebCompat extension could have obtained a persistent UUID that identified the browser, and persisted between containers and normal/private browsing mode, but not profiles. This vulnerability was

How urgent is CVE-2025-6425?

Priority 21/100. No elevated risk signals yet.

Software pages

Mozilla Firefox vulnerabilities

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References

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