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Fencer Vulns
high 7.5

CVE-2020-12391 json

Documents formed using data: URLs in an OBJECT element failed to inherit the CSP of the creating context.

published 2020-05-26 6 y ago modified 2026-06-17 4 mo ago also EUVD-2020-4703

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.5%
EPSS 1.5% chance of exploitation in 30 days, percentile 73%
public exploits
0
none known

Summary

Documents formed using data: URLs in an OBJECT element failed to inherit the CSP of the creating context. This allowed the execution of scripts that should have been blocked, albeit with a unique opaque origin. This vulnerability affects Firefox < 76.

Patch / fix

  • Mozilla Firefox 76
  • firefox Ubuntu 16.04 LTS 76.0+build2-0ubuntu0.16.04.1
  • firefox Ubuntu 18.04 LTS 76.0+build2-0ubuntu0.18.04.1
  • firefox Ubuntu 20.04 LTS 76.0+build2-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2020-12391

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 76.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 76.0-r0

alpine advisories ALPINE-CVE-2020-12391

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

  • firefox Arch Linux 76.0-1

arch linux advisories AVG-1148

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-2020-12391 updated cvss 7.5

Mozilla: Content-Security-Policy bypass using object elements

  • Red Hat Enterprise Linux 5 firefox Red Hat Enterprise Linux 6 firefox
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 firefox Red Hat Enterprise Linux 8 firefox
    affected: no fix planned “Will not fix”

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

1.46% chance of exploitation in the next 30 days, higher than 73% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:P/A:N

Affected products

  • Mozilla Firefox

Classification

Weakness

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.