CVE-2021-23997

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-24 · updated 2026-06-17
Weakness: CWE-681

Description

Due to unexpected data type conversions, a use-after-free could have occurred when interacting with the font cache. We presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability affects Firefox < 88.

Affected products

Mozilla Firefox: before 88.0 — fixed in 88.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 88.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1701942
https://www.mozilla.org/security/advisories/mfsa2021-16/
https://bugzilla.mozilla.org/show_bug.cgi?id=1701942
https://www.mozilla.org/security/advisories/mfsa2021-16/

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