NVD / CVE Program· CNA mozilla

CVE-2020-12421: When performing add-on updates, certificate chains terminating in non-built-in-roots were rejected (even if they were legitimately added by…

MediumCVSS 6.5 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 27/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 1.8% (FIRST EPSS); higher than 79.3% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
Fixed version: firefox-esr (Alpine:v3.11) 68.10.0-r0; firefox (Alpine:v3.12) 78.0-r0; mozjs68 (Alpine:v3.12) 68.10.0-r0.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to firefox-esr (Alpine:v3.11) 68.10.0-r0; firefox (Alpine:v3.12) 78.0-r0; mozjs68 (Alpine:v3.12) 68.10.0-r0 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

When performing add-on updates, certificate chains terminating in non-built-in-roots were rejected (even if they were legitimately added by an administrator.) This could have caused add-ons to become out-of-date silently without notification to the user. This vulnerability affects Firefox ESR < 68.10, Firefox < 78, and Thunderbird < 68.10.0.

Published: Jul 9, 2020
Updated: Jun 16, 2026
EPSS: 1.8% · 79th percentile
CWE: CWE-295

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 26 / 40 · 6.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 1 / 30 · 1.8%

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Check your site's encryptionRun the SSL check

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
mozilla	firefox	cpe:2.3:a:mozilla:firefox
mozilla	firefox esr	cpe:2.3:a:mozilla:firefox_esr
mozilla	thunderbird	cpe:2.3:a:mozilla:thunderbird
canonical	ubuntu linux	cpe:2.3:o:canonical:ubuntu_linux

Check your site's encryption

This vulnerability is about certificate validation or weak cryptography. The free SSL checker tests your certificate, enabled TLS versions and weak ciphers.

Run the SSL check

Versions reported by the vendor

Affected version ranges reported by the assigning authority (mozilla). Independent of NVD's CPE analysis and usually ahead of it.

Mozilla Firefox
- unspecified and later · before 78affected
Mozilla Firefox ESR
- unspecified and later · before 68.10affected
Mozilla Thunderbird
- unspecified and later · before 68.10.0affected

Affected versions · NVD (7)

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

canonical ubuntu linux16.04
canonical ubuntu linux18.04
canonical ubuntu linux19.10
canonical ubuntu linux20.04
mozilla firefoxbefore 78.0
mozilla firefox esrbefore 68.10.0
mozilla thunderbirdbefore 68.10.0

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Alpine:v3.11	firefox-esr	before 68.10.0-r0	68.10.0-r0
Alpine:v3.12	firefox	before 78.0-r0	78.0-r0
Alpine:v3.12	mozjs68	before 68.10.0-r0	68.10.0-r0
Alpine:v3.16	thunderbird	before 68.10.0-r0	68.10.0-r0
Alpine:v3.21	librewolf	before 78.0-r0	78.0-r0
Debian:10	firefox-esr	before 68.10.0esr-1~deb10u1	68.10.0esr-1~deb10u1
Debian:10	thunderbird	before 1:68.10.0-1~deb10u1	1:68.10.0-1~deb10u1
Debian:12	firefox-esr	before 68.10.0esr-1	68.10.0esr-1
Debian:12	thunderbird	before 1:68.10.0-1	1:68.10.0-1
Debian:9	firefox-esr	before 68.10.0esr-1~deb9u1	68.10.0esr-1~deb9u1
Debian:9	thunderbird	before 1:68.10.0-1~deb9u1	1:68.10.0-1~deb9u1
openSUSE:Leap 15.1	MozillaFirefox	before 78.0.1-lp151.2.53.1	78.0.1-lp151.2.53.1
openSUSE:Leap 15.1	MozillaThunderbird	before 68.10.0-lp151.2.44.2	68.10.0-lp151.2.44.2
openSUSE:Leap 15.2	MozillaFirefox	before 78.0.1-lp152.2.5.1	78.0.1-lp152.2.5.1
openSUSE:Leap 15.2	MozillaThunderbird	before 68.10.0-lp152.2.4.1	68.10.0-lp152.2.4.1
Red Hat:enterprise_linux:6::client	firefox	before 0:68.10.0-1.el6_10	0:68.10.0-1.el6_10
Red Hat:enterprise_linux:6::client	firefox-debuginfo	before 0:68.10.0-1.el6_10	0:68.10.0-1.el6_10
Red Hat:enterprise_linux:6::client	thunderbird	before 0:68.10.0-1.el6_10	0:68.10.0-1.el6_10
Red Hat:enterprise_linux:6::client	thunderbird-debuginfo	before 0:68.10.0-1.el6_10	0:68.10.0-1.el6_10
Red Hat:enterprise_linux:7::client	firefox	before 0:68.10.0-1.el7_8	0:68.10.0-1.el7_8
Red Hat:enterprise_linux:7::client	firefox-debuginfo	before 0:68.10.0-1.el7_8	0:68.10.0-1.el7_8
Red Hat:enterprise_linux:7::client	thunderbird	before 0:68.10.0-1.el7_8	0:68.10.0-1.el7_8
Red Hat:enterprise_linux:7::client	thunderbird-debuginfo	before 0:68.10.0-1.el7_8	0:68.10.0-1.el7_8
Red Hat:enterprise_linux:8::appstream	firefox	before 0:68.10.0-1.el8_2	0:68.10.0-1.el8_2

+24

Same product

mozilla: all records

Other highest-scoring records for the same primary product.

CVE-2010-3765Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x…KEV
94Now
CVE-2019-11708Insufficient vetting of parameters passed with the Prompt:Open IPC message between child and parent processes can result in the…KEV
87Now
CVE-2015-4495The PDF reader in Mozilla Firefox before 39.0.3, Firefox ESR 38.x before 38.1.1, and Firefox OS before 2.2 allows remote attackers to…KEV
86Now

Published before and after this one in the same product

← EarlierCVE-2020-12419Jul 9, 2020 · When processing callbacks that occurred during window flushing in the parent process, the associated window may die; causing a…
36Monitor
← EarlierCVE-2020-12420Jul 9, 2020 · When trying to connect to a STUN server, a race condition could have caused a use-after-free of a pointer, leading to memory corruption and…
36Monitor
Later →CVE-2020-12422Jul 9, 2020 · In non-standard configurations, a JPEG image created by JavaScript could have caused an internal variable to overflow, resulting in an out…
36Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
alpine:firefox	78.0-r0 · Alpine:v3.12	Package registry (OSV)
alpine:firefox-esr	68.10.0-r0 · Alpine:v3.11	Package registry (OSV)
alpine:librewolf	78.0-r0 · Alpine:v3.21	Package registry (OSV)
alpine:mozjs68	68.10.0-r0 · Alpine:v3.12	Package registry (OSV)
alpine:thunderbird	68.10.0-r0 · Alpine:v3.16	Package registry (OSV)
debian:firefox-esr	68.10.0esr-1 · Debian:12	Package registry (OSV)
debian:thunderbird	1:68.10.0-1 · Debian:12	Package registry (OSV)
opensuse:MozillaFirefox	78.0.1-lp152.2.5.1 · openSUSE:Leap 15.2	Package registry (OSV)
opensuse:MozillaThunderbird	68.10.0-lp151.2.44.2 · openSUSE:Leap 15.1	Package registry (OSV)
red hat:firefox	0:68.10.0-1.el6_10 · Red Hat:enterprise_linux:6::client	Package registry (OSV)
red hat:firefox-debuginfo	0:68.10.0-1.el6_10 · Red Hat:enterprise_linux:6::client	Package registry (OSV)
red hat:firefox-debugsource	0:68.10.0-1.el8_0 · Red Hat:rhel_e4s:8.0::appstream	Package registry (OSV)
red hat:thunderbird	0:68.10.0-1.el7_8 · Red Hat:enterprise_linux:7::client	Package registry (OSV)
red hat:thunderbird-debuginfo	0:68.10.0-1.el7_8 · Red Hat:enterprise_linux:7::client	Package registry (OSV)
red hat:thunderbird-debugsource	0:68.10.0-1.el8_1 · Red Hat:rhel_eus:8.1::appstream	Package registry (OSV)
suse:MozillaFirefox	78.0.1-78.80.2 · SUSE:Linux Enterprise Server 11 SP4-LTSS	Package registry (OSV)
suse:MozillaFirefox-branding-SLE	78-4.14.1 · SUSE:Linux Enterprise Module for Desktop Applications 15 SP1	Package registry (OSV)
suse:MozillaFirefox-branding-SLED	78-21.12.1 · SUSE:Linux Enterprise Server 11 SP4-LTSS	Package registry (OSV)
suse:MozillaThunderbird	68.10.0-3.88.1 · SUSE:Linux Enterprise Workstation Extension 15 SP1	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-20-534 · Jul 16, 2020(Thunderbird Zafiyeti)

All national notices →

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
A user must open a link or visit a page.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: high · data or configuration can be modified
Availability: none

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: Required
Scope: Unchanged
Confidentiality impact: None
Integrity impact: High
Availability impact: None

Weakness class (CWE)

CWE-295 · Improper Certificate Validation

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

nvd-primary

Root cause

A certificate validation error is silently swallowed instead of terminating the connection. Often, code added for a test environment makes its way into production.

The bug in code

The whole CWE-295 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

kotlin

1override fun checkServerTrusted(chain: Array<X509Certificate>, type: String) {
2  // Left empty for the test environment
3}

Fixed

kotlin

1val client = OkHttpClient.Builder()
2  .certificatePinner(
3    CertificatePinner.Builder()
4      .add("api.sirius.example", "sha256/…")
5      .build()
6  ).build()

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log (1)

Fix✗ → ✓Sep 28, 2026, 10:47 PM UTC

For records you follow, these changes also arrive as notifications. →

References

lists.opensuse.org/opensuse-security-announce/2020-07/msg00023.html

Show all references (10 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records