medium 6.1

CVE-2019-11763 json

Failure to correctly handle null bytes when processing HTML entities resulted in Firefox incorrectly parsing these entities.

published 2020-01-08 6y ago modified 2026-06-17 4mo ago also EUVD-2019-3433

cvss: 6.1; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.1%; EPSS 1.1% chance of exploitation in 30 days, percentile 67%
public exploits: 0; none known

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.

Patch / fix

fixed in 3 distros 7

mozilla firefox 70.0
mozilla firefox_esr 68.2
mozilla thunderbird 68.2

debian ubuntu red hat suse opensuse alpine arch linux

firefox-esr Debian 14, Debian 13, Debian 12 68.2.0esr-1
thunderbird Debian 14, Debian 13, Debian 12 1:68.2.1-1

debian advisories DEBIAN-CVE-2019-11763

firefox Ubuntu 16.04 LTS 70.0+build2-0ubuntu0.16.04.1
firefox Ubuntu 18.04 LTS 70.0+build2-0ubuntu0.18.04.1
firefox Ubuntu 20.04 LTS 70.0+build2-0ubuntu1
thunderbird Ubuntu 16.04 LTS 1:68.7.0+build1-0ubuntu0.16.04.2
thunderbird Ubuntu 18.04 LTS 1:68.2.1+build1-0ubuntu0.18.04.1

ubuntu advisories UBUNTU-CVE-2019-11763

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

thunderbird RHEL 6 68.2.0-2.el6_10
firefox RHEL 6 68.2.0-4.el6_10
thunderbird RHEL 7 68.2.0-1.el7_7
thunderbird RHEL 8 68.2.0-1.el8_0
firefox RHEL 7 68.2.0-1.el7_7
firefox RHEL 8 68.2.0-2.el8_0

red hat advisories RHSA-2019:3756 RHSA-2019:3281 RHSA-2019:3210 RHSA-2019:3237 RHSA-2019:3193 RHSA-2019:3196

MozillaThunderbird SLE Workstation Extension 15 SP1, SLE Workstation Extension 15 68.2.1-3.58.1
MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +17 more 68.2.0-109.95.2
MozillaFirefox-branding-SLE SLE Module for Desktop Applications 15 SP1, SLE Module for Desktop Applications 15 68-4.11.2
MozillaFirefox SLE Module for Desktop Applications 15 SP1, SLE Module for Desktop Applications 15 68.2.0-3.59.1
firefox-atk SLES 11 SP4-LTSS 2.26.1-2.8.4
mozilla-nss SLES 11 SP4-LTSS 3.45-38.9.3
firefox-gtk3 SLES 11 SP4-LTSS 3.10.9-2.15.3
mozilla-nspr SLES 11 SP4-LTSS 4.21-29.6.1

suse advisories SUSE-SU-2019:14246-1 SUSE-SU-2019:2912-1 SUSE-SU-2019:2872-1 SUSE-SU-2019:2871-1

firefox-esr openSUSE Tumbleweed 128.5.1-1.1
MozillaFirefox openSUSE Tumbleweed 92.0-1.2
MozillaThunderbird openSUSE Tumbleweed 91.1.1-1.1
MozillaThunderbird openSUSE Leap 15.0 68.2.1-lp150.3.54.1
MozillaFirefox openSUSE Leap 15.0 68.2.0-lp150.3.71.1
firefox-esr-branding-openSUSE openSUSE Leap 15.0 68-lp150.3.3.1
MozillaFirefox-branding-openSUSE openSUSE Leap 15.0 68-lp150.3.3.1
MozillaThunderbird openSUSE Leap 15.1 68.2.1-lp151.2.16.1

opensuse advisories openSUSE-SU-2024:14572-1 openSUSE-SU-2024:10600-1 openSUSE-SU-2024:10601-1 openSUSE-SU-2019:2464-1 openSUSE-SU-2019:2459-1 openSUSE-SU-2019:2452-1

firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 70.0-r0
librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 70.0-r0
firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +10 more 68.2.0-r0

alpine advisories ALPINE-CVE-2019-11763

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

thunderbird Arch Linux 68.2.0-1
firefox Arch Linux 70.0-1

arch linux advisories AVG-1054 AVG-1055

Is CVE-2019-11763 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2019-11763 updated 2026-11-05 cvss 6.1

Mozilla: Incorrect HTML parsing results in XSS bypass technique

Red Hat Enterprise Linux 5 firefox, thunderbird
affected: no fix planned “Out of support scope”
Red Hat Enterprise Linux AppStream (v. 8) firefox 68.2.0-2.el8_0, thunderbird 68.2.0-1.el8_0
fixed: vendor fix RHSA-2019:3196
Red Hat Enterprise Linux Client (v. 7) firefox 68.2.0-1.el7_7, thunderbird 68.2.0-1.el7_7 Red Hat Enterprise Linux Client Optional (v. 7) firefox 68.2.0-1.el7_7
fixed: vendor fix RHSA-2019:3193
Red Hat Enterprise Linux Desktop (v. 6) firefox 68.2.0-4.el6_10, thunderbird 68.2.0-2.el6_10 Red Hat Enterprise Linux Desktop Optional (v. 6) firefox 68.2.0-4.el6_10 Red Hat Enterprise Linux HPC Node Optional (v. 6) firefox 68.2.0-4.el6_10 Red Hat Enterprise Linux Server (v. 6) firefox 68.2.0-4.el6_10
fixed: vendor fix RHSA-2019:3281
Red Hat Enterprise Linux Server (v. 7) firefox 68.2.0-1.el7_7
fixed: vendor fix RHSA-2019:3193
Red Hat Enterprise Linux Server Optional (v. 6) firefox 68.2.0-4.el6_10, thunderbird 68.2.0-2.el6_10
fixed: vendor fix RHSA-2019:3281
Red Hat Enterprise Linux Server Optional (v. 7) firefox 68.2.0-1.el7_7, thunderbird 68.2.0-1.el7_7
fixed: vendor fix RHSA-2019:3193
Red Hat Enterprise Linux Workstation (v. 6) firefox 68.2.0-4.el6_10, thunderbird 68.2.0-2.el6_10
fixed: vendor fix RHSA-2019:3281

show 3 more

Red Hat Enterprise Linux Workstation (v. 7) firefox 68.2.0-1.el7_7, thunderbird 68.2.0-1.el7_7
fixed: vendor fix RHSA-2019:3193
Red Hat Enterprise Linux Workstation Optional (v. 6) firefox 68.2.0-4.el6_10
fixed: vendor fix RHSA-2019:3281
Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 68.2.0-1.el7_7
fixed: vendor fix RHSA-2019:3193

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.15% chance of exploitation in the next 30 days, higher than 67% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
NVD	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD	2.0	4.3	AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

Mozilla Firefox
Mozilla Thunderbird
Mozilla Firefox ESR

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

security.gentoo.org /glsa/202003-10
vendor-advisory, third-party-advisory
usn.ubuntu.com /4335-1/
vendor-advisory, third-party-advisory
mozilla.org /security/advisories/mfsa2019-35/
vendor-advisory
mozilla.org /security/advisories/mfsa2019-33/
vendor-advisory
mozilla.org /security/advisories/mfsa2019-34/
vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=1584216
issue-tracking, permissions-required

Sources

CVE List CVE-2019-11763
NVD CVE-2019-11763

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

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