CVE-2019-11763

Name: CVE-2019-11763
Creator: NVD / NIST
Published: 2020-01-08T20:15:12.953+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.1/10EPSS 0.99%

Last modified Jun 17, 2026

CVE-2019-11763 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. 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. EPSS estimates a 0.99% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

6.1/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS Probability

0.99%

58.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 70.0
Mozilla	Firefox Esr	< 68.2
Mozilla	Thunderbird	< 68.2
Canonical	Ubuntu Linux	16.04

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1584216Issue Tracking, Permissions Required
https://security.gentoo.org/glsa/202003-10Third Party Advisory
https://usn.ubuntu.com/4335-1/Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2019-33/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2019-34/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2019-35/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1584216Issue Tracking, Permissions Required
https://security.gentoo.org/glsa/202003-10Third Party Advisory
https://usn.ubuntu.com/4335-1/Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2019-33/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2019-34/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2019-35/Vendor Advisory

Timeline

Published: Jan 8, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2019-11763?

How severe is CVE-2019-11763?

CVE-2019-11763 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 0.99% probability of exploitation in the next 30 days.

How do I fix CVE-2019-11763?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2019-11763?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST