What’s Vulnerable › Vulnerabilities

CVE-2020-26973

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-01-07 · updated 2026-06-17

Description

Certain input to the CSS Sanitizer confused it, resulting in incorrect components being removed. This could have been used as a sanitizer bypass. 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=1680084
• 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=1680084
• 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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