CVE-2020-26967: Mozilla Firefox

Medium severity, CVSS 6.5. EPSS: 0.9% chance of exploitation in the next 30 days.

When listening for page changes with a Mutation Observer, a malicious web page could confuse Firefox Screenshots into interacting with elements other than those that it injected into the page. This would lead to internal errors and unexpected behavior in the Screenshots code. This vulnerability affects Firefox < 83.

Affected products

• Mozilla Firefox: before 83.0 (fixed in 83.0)

Published 2020-12-09. Last modified 2026-06-17.