What’s Vulnerable › Vulnerabilities

CVE-2020-12387

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-05-26 · updated 2026-06-17
• Weakness: CWE-362

Description

A race condition when running shutdown code for Web Worker led to a use-after-free vulnerability. This resulted in a potentially exploitable crash. This vulnerability affects Firefox ESR < 68.8, Firefox < 76, and Thunderbird < 68.8.0.

Affected products

• Mozilla Firefox: before 76.0 — fixed in 76.0
• Mozilla Firefox ESR: before 68.8.0 — fixed in 68.8.0
• Mozilla Thunderbird: before 68.8.0 — fixed in 68.8.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 76.0; Mozilla Firefox ESR 68.8.0; Mozilla Thunderbird 68.8.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1545345
• https://security.gentoo.org/glsa/202005-03
• https://security.gentoo.org/glsa/202005-04
• https://usn.ubuntu.com/4373-1/
• https://www.mozilla.org/security/advisories/mfsa2020-16/
• https://www.mozilla.org/security/advisories/mfsa2020-17/
• https://www.mozilla.org/security/advisories/mfsa2020-18/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1545345
• https://security.gentoo.org/glsa/202005-03
• https://security.gentoo.org/glsa/202005-04
• https://usn.ubuntu.com/4373-1/
• https://www.mozilla.org/security/advisories/mfsa2020-16/

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