How severe is CVE-2026-8391?

CVE-2026-8391 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2026-8391 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (22nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-8391?

CVE-2026-8391 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-8391?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-8391 have an EU (EUVD) identifier?

Yes. CVE-2026-8391 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29466.

When was CVE-2026-8391 published?

CVE-2026-8391 was published on 2026-05-12 and last updated on 2026-06-30.

CVE-2026-8391

CVE-2026-8391 is a medium-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 0% (22nd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-29466
Weakness: CWE-20
Affected product: Mozilla Firefox
Published: 2026-05-12
Last modified: 2026-06-30

Description

Other issue in the JavaScript Engine component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.

Frequently asked questions

What is CVE-2026-8391?: Other issue in the JavaScript Engine component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.
How severe is CVE-2026-8391?: CVE-2026-8391 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2026-8391 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (22nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-8391?: CVE-2026-8391 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-8391?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-8391 have an EU (EUVD) identifier?: Yes. CVE-2026-8391 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29466.
When was CVE-2026-8391 published?: CVE-2026-8391 was published on 2026-05-12 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*

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