What’s Vulnerable › Vulnerabilities

CVE-2020-26951

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-12-09 · updated 2026-06-17
• Weakness: CWE-79

Description

A parsing and event loading mismatch in Firefox's SVG code could have allowed load events to fire, even after sanitization. An attacker already capable of exploiting an XSS vulnerability in privileged internal pages could have used this attack to bypass our built-in sanitizer. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

Affected products

• Mozilla Firefox: before 83.0 — fixed in 83.0
• Mozilla Firefox ESR: before 78.5 — fixed in 78.5
• Mozilla Thunderbird: before 78.5 — fixed in 78.5

How to fix

Upgrade to a fixed version: Mozilla Firefox 83.0; Mozilla Firefox ESR 78.5; Mozilla Thunderbird 78.5. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1667113
• https://www.mozilla.org/security/advisories/mfsa2020-50/
• https://www.mozilla.org/security/advisories/mfsa2020-51/
• https://www.mozilla.org/security/advisories/mfsa2020-52/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1667113
• https://www.mozilla.org/security/advisories/mfsa2020-50/
• https://www.mozilla.org/security/advisories/mfsa2020-51/
• https://www.mozilla.org/security/advisories/mfsa2020-52/

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