CVE-2021-23999
CVSS v3
8.8
HIGH
EPSS Score
1.4 %
exploit probability, as of 2026-09-25
CISA KEV
No
known exploited
Exploitation
—
SSVC status
Description
If a Blob URL was loaded through some unusual user interaction, it could have been loaded by the System Principal and granted additional privileges that should not be granted to web content. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.
Technical details
- Published
- 2021-06-24
Frequently asked questions
What is CVE-2021-23999?
If a Blob URL was loaded through some unusual user interaction, it could have been loaded by the System Principal and granted additional privileges that should not be granted to web content. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.
Is CVE-2021-23999 actively exploited?
Active exploitation of CVE-2021-23999 has not been confirmed. Its EPSS score was 1.4% on 2026-09-25, the estimated probability of exploitation in the next 30 days.
What is the CVSS score for CVE-2021-23999?
CVE-2021-23999 has a CVSS v3 base score of 8.8 (HIGH severity).
Is CVE-2021-23999 affecting your environment?
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