How severe is CVE-2021-29961?

CVE-2021-29961 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2021-29961 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (51st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-29961?

CVE-2021-29961 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-29961?

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

When was CVE-2021-29961 published?

CVE-2021-29961 was published on 2021-06-24 and last updated on 2026-06-17.

CVE-2021-29961

CVE-2021-29961 is a medium-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 4.3. 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-863.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
CVSS v2: 4.3
EPSS exploit prediction: 1% (51st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-863
Affected product: Mozilla Firefox
Published: 2021-06-24
Last modified: 2026-06-17

Description

When styling and rendering an oversized `<select>` element, Firefox did not apply correct clipping which allowed an attacker to paint over the user interface. This vulnerability affects Firefox < 89.

Frequently asked questions

What is CVE-2021-29961?: When styling and rendering an oversized `<select>` element, Firefox did not apply correct clipping which allowed an attacker to paint over the user interface. This vulnerability affects Firefox < 89.
How severe is CVE-2021-29961?: CVE-2021-29961 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2021-29961 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (51st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-29961?: CVE-2021-29961 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-29961?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-29961 published?: CVE-2021-29961 was published on 2021-06-24 and last updated on 2026-06-17.

References

Affected products (1)

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

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