Unsanitized output in the browser UI leaves HTML tags in place and can result in arbitrary code execution in Firefox before version 58.0.1.

published 2019-04-26 7 y ago modified 2026-06-17 4 mo ago also EUVD-2018-16910

cvss: 6.1; version 3.0, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.0%; EPSS 1.0% chance of exploitation in 30 days, percentile 63%
public exploits: 0; none known

Patch / fix

fixed in 1 distros 1

mozilla firefox 58.0.1

firefox Ubuntu 14.04 LTS 58.0.1+build1-0ubuntu0.14.04.1
firefox Ubuntu 16.04 LTS 58.0.1+build1-0ubuntu0.16.04.1
firefox Ubuntu 18.04 LTS 59.0.1+build1-0ubuntu1

ubuntu advisories UBUNTU-CVE-2018-5124

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

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-2018-5124 updated 2026-11-04 cvss 6.1

firefox: Unsanitized output in browser UI can lead to arbitrary code execution

Red Hat Enterprise Linux 5 firefox Red Hat Enterprise Linux 6 firefox Red Hat Enterprise Linux 7 firefox
not affected: vulnerable code not present

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

1.01% chance of exploitation in the next 30 days, higher than 63% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
NVD	3.0	6.1	CVSS:3.0/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

n/a Firefox

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

mozilla.org /en-US/security/advisories/mfsa2018-05/
vendor-advisory

Sources

CVE List CVE-2018-5124
NVD CVE-2018-5124

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.

Summary