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Fencer Vulns
medium 4.3

CVE-2020-15665 json

Firefox did not reset the address bar after the beforeunload dialog was shown if the user chose to remain on the page.

published 2020-10-01 6 y ago modified 2026-06-17 4 mo ago also EUVD-2020-7652

cvss
4.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 52%
public exploits
0
none known

Summary

Firefox did not reset the address bar after the beforeunload dialog was shown if the user chose to remain on the page. This could have resulted in an incorrect URL being shown when used in conjunction with other unexpected browser behaviors. This vulnerability affects Firefox < 80.

Patch / fix

  • Mozilla Firefox 80
  • firefox Ubuntu 16.04 LTS 80.0+build2-0ubuntu0.16.04.1
  • firefox Ubuntu 18.04 LTS 80.0+build2-0ubuntu0.18.04.1
  • firefox Ubuntu 20.04 LTS 80.0+build2-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2020-15665

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 92.0-1.2

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 80.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 80.0-r0

alpine advisories ALPINE-CVE-2020-15665

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org 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-2020-15665 updated cvss 4.7

firefox: Address bar not reset when choosing to stay on a page after the beforeunload dialog is shown

  • Red Hat Enterprise Linux 5 firefox
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 6 firefox Red Hat Enterprise Linux 7 firefox Red Hat Enterprise Linux 8 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

0.69% chance of exploitation in the next 30 days, higher than 52% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugzilla.mozilla.org https://bugzilla.mozilla.org/show_bug.cgi?id=1651636 referenced PoC, tagged "exploit" by a source, unverified

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
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

  • Mozilla Firefox

References

Sources

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.