CVE-2020-12403

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.

Published: 2021-05-27 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-12403 is rated Moderate Risk (62/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 0.72%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2020-12403

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-28 0.58% 0.72% +0.14%
2 2026-02-24 0.19% 0.58% +0.39%
3 2025-11-21 — 0.19% —

Full EPSS history (16 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-12403

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.1 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.2 [email protected]
6.4 2.0 MEDIUM
AV:N/AC:L/Au:N/C:P/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 4.9 [email protected]

Weakness enumeration for CVE-2020-12403

OS Trackers for CVE-2020-12403

vendor priority summary link
alpine critical CVE-2020-12403: 1 source package rows (nss); 40 state rows across 10 repos (3.11-main, 3.12-main, 3.17-community, 3.18-community, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-community, edge-main); fixed 9, open 31. https://security.alpinelinux.org/vuln/CVE-2020-12403
debian not yet assigned CVE-2020-12403 not yet assigned priority: Debian including 1 source packages (nss), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2020-12403
gentoo normal CVE-2020-12403: 1 GLSA(s) (202008-08), 1 atom(s) (dev-libs/nss); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2020-12403
redhat medium — https://access.redhat.com/security/cve/CVE-2020-12403
ubuntu medium CVE-2020-12403 medium priority: Ubuntu including 1 source packages (nss), 5 status rows across 5 suites (bionic, focal, trusty, upstream, xenial): released 5. https://ubuntu.com/security/CVE-2020-12403

Affected software / configurations for CVE-2020-12403

Vendor Product Version Raw CPE
mozilla nss < 3.55 cpe:2.3:a:mozilla:nss:*:*:*:*:*:*:*:*

References for CVE-2020-12403

cvelogic Threat Intelligence