What’s Vulnerable › Vulnerabilities

CVE-2020-26974

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-01-07 · updated 2026-06-17
• Weakness: CWE-787

Description

When flex-basis was used on a table wrapper, a StyleGenericFlexBasis object could have been incorrectly cast to the wrong type. This resulted in a heap user-after-free, memory corruption, and a potentially exploitable crash. This vulnerability affects Firefox < 84, Thunderbird < 78.6, and Firefox ESR < 78.6.

Affected products

• Mozilla Firefox: before 84.0 — fixed in 84.0
• Mozilla Firefox ESR: before 78.6.0 — fixed in 78.6.0
• Mozilla Thunderbird: before 78.6.0 — fixed in 78.6.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 84.0; Mozilla Firefox ESR 78.6.0; Mozilla Thunderbird 78.6.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1681022
• https://www.mozilla.org/security/advisories/mfsa2020-54/
• https://www.mozilla.org/security/advisories/mfsa2020-55/
• https://www.mozilla.org/security/advisories/mfsa2020-56/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1681022
• https://www.mozilla.org/security/advisories/mfsa2020-54/
• https://www.mozilla.org/security/advisories/mfsa2020-55/
• https://www.mozilla.org/security/advisories/mfsa2020-56/

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