Under certain conditions, Firefox did not display a warning when a user attempted to navigate to a new protocol handler.

published 2023-12-19 2 y ago modified 2026-06-17 4 mo ago also EUVD-2023-59075

cvss: 4.3; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.5%; EPSS 0.5% chance of exploitation in 30 days, percentile 42%
public exploits: 0; none known

Under certain conditions, Firefox did not display a warning when a user attempted to navigate to a new protocol handler. This vulnerability affects Firefox < 121.

Patch / fix

fixed in 1 distros 2

Mozilla Firefox 121

ubuntu opensuse

firefox Ubuntu 20.04 LTS 121.0+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2023-6871

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

firefox-esr openSUSE Tumbleweed 128.5.1-1.1
MozillaFirefox openSUSE Tumbleweed 121.0-1.1

opensuse advisories openSUSE-SU-2024:14572-1 openSUSE-SU-2024:13531-1

Exploit prediction

0.49% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Affected products

Mozilla Firefox

References

mozilla.org /security/advisories/mfsa2023-56/
vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=1828334
issue-tracking, permissions-required
security.gentoo.org /glsa/202401-10
third-party-advisory

Sources

CVE List CVE-2023-6871
NVD CVE-2023-6871

Fencer Vulns 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