CVE-2021-23975: Mozilla Firefox

Medium severity, CVSS 6.5. EPSS: 1% chance of exploitation in the next 30 days.

The developer page about:memory has a Measure function for exploring what object types the browser has allocated and their sizes. When this function was invoked we incorrectly called the sizeof function, instead of using the API method that checks for invalid pointers. This vulnerability affects Firefox < 86.

Affected products

• Mozilla Firefox: before 86.0 (fixed in 86.0)

Published 2021-02-26. Last modified 2026-06-17.