How severe is CVE-2021-23998?

CVE-2021-23998 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2021-23998 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-23998?

CVE-2021-23998 primarily affects Mozilla Firefox. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-23998?

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

When was CVE-2021-23998 published?

CVE-2021-23998 was published on 2021-06-24 and last updated on 2026-06-17.

CVE-2021-23998

CVE-2021-23998 is a medium-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 6.5. 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-345.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v2: 4.3
EPSS exploit prediction: 1% (42nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-345
Affected product: Mozilla Firefox
Published: 2021-06-24
Last modified: 2026-06-17

Description

Through complicated navigations with new windows, an HTTP page could have inherited a secure lock icon from an HTTPS page. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.

Frequently asked questions

What is CVE-2021-23998?: Through complicated navigations with new windows, an HTTP page could have inherited a secure lock icon from an HTTPS page. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.
How severe is CVE-2021-23998?: CVE-2021-23998 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2021-23998 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-23998?: CVE-2021-23998 primarily affects Mozilla Firefox. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-23998?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-23998 published?: CVE-2021-23998 was published on 2021-06-24 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

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