How severe is CVE-2020-12406?

CVE-2020-12406 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2020-12406 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (61st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-12406?

CVE-2020-12406 primarily affects Mozilla Firefox. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2020-12406?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2020-12406 published?

CVE-2020-12406 was published on 2020-07-09 and last updated on 2026-06-17.

CVE-2020-12406

CVE-2020-12406 is a high-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-345.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 9.3
EPSS exploit prediction: 1% (61st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-345
Affected product: Mozilla Firefox
Published: 2020-07-09
Last modified: 2026-06-17

Description

Mozilla Developer Iain Ireland discovered a missing type check during unboxed objects removal, resulting in a crash. We presume that with enough effort that it could be exploited to run arbitrary code. This vulnerability affects Thunderbird < 68.9.0, Firefox < 77, and Firefox ESR < 68.9.

Frequently asked questions

What is CVE-2020-12406?: Mozilla Developer Iain Ireland discovered a missing type check during unboxed objects removal, resulting in a crash. We presume that with enough effort that it could be exploited to run arbitrary code. This vulnerability affects Thunderbird < 68.9.0, Firefox < 77, and Firefox ESR < 68.9.
How severe is CVE-2020-12406?: CVE-2020-12406 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2020-12406 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (61st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-12406?: CVE-2020-12406 primarily affects Mozilla Firefox. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-12406?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2020-12406 published?: CVE-2020-12406 was published on 2020-07-09 and last updated on 2026-06-17.

References

Affected products (7)

cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:esm:*:*:*
cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*
cpe:2.3:o:canonical:ubuntu_linux:19.10:*:*:*:*:*:*:*
cpe:2.3:o:canonical:ubuntu_linux:20.04:*:*:*:lts:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

168.90.177.192 (ipv4-addr)