What’s Vulnerable › Vulnerabilities

CVE-2019-11763

• 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: 2020-01-08 · updated 2026-06-17
• Weakness: CWE-79

Description

Failure to correctly handle null bytes when processing HTML entities resulted in Firefox incorrectly parsing these entities. This could have led to HTML comment text being treated as HTML which could have led to XSS in a web application under certain conditions. It could have also led to HTML entities being masked from filters - enabling the use of entities to mask the actual characters of interest from filters. This vulnerability affects Firefox < 70, Thunderbird < 68.2, and Firefox ESR < 68.2.

Affected products

• Canonical Ubuntu Linux: 16.04
• Mozilla Firefox: before 70.0 — fixed in 70.0
• Mozilla Firefox ESR: before 68.2 — fixed in 68.2
• Mozilla Thunderbird: before 68.2 — fixed in 68.2

How to fix

Upgrade to a fixed version: Mozilla Firefox 70.0; Mozilla Firefox ESR 68.2; Mozilla Thunderbird 68.2. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1584216
• https://security.gentoo.org/glsa/202003-10
• https://usn.ubuntu.com/4335-1/
• https://www.mozilla.org/security/advisories/mfsa2019-33/
• https://www.mozilla.org/security/advisories/mfsa2019-34/
• https://www.mozilla.org/security/advisories/mfsa2019-35/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1584216
• https://security.gentoo.org/glsa/202003-10
• https://usn.ubuntu.com/4335-1/
• https://www.mozilla.org/security/advisories/mfsa2019-33/
• https://www.mozilla.org/security/advisories/mfsa2019-34/
• https://www.mozilla.org/security/advisories/mfsa2019-35/

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