CVE-2020-12403: Mozilla Nss

Critical severity, CVSS 9.1. EPSS: 1.5% chance of exploitation in the next 30 days.

A flaw was found in the way CHACHA20-POLY1305 was implemented in NSS in versions before 3.55. When using multi-part Chacha20, it could cause out-of-bounds reads. This issue was fixed by explicitly disabling multi-part ChaCha20 (which was not functioning correctly) and strictly enforcing tag length. The highest threat from this vulnerability is to confidentiality and system availability.

Affected products

• Mozilla Nss: before 3.55 (fixed in 3.55)

Published 2021-05-27. Last modified 2026-06-17.