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Fencer Intel
medium 6.5

CVE-2021-43541 json

When invoking protocol handlers for external protocols, a supplied parameter URL containing spaces was not properly escaped.

published 4y ago modified 4mo ago also EUVD-2021-30470

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.6%
EPSS 1.6% chance of exploitation in 30 days, percentile 76%
public exploits
0
none known

Summary

When invoking protocol handlers for external protocols, a supplied parameter URL containing spaces was not properly escaped. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

Patch / fix

  • Mozilla Thunderbird 91.4.0
  • Mozilla Firefox ESR 91.4.0
  • Mozilla Firefox 95
  • firefox-esr Debian 14, Debian 13, Debian 12 91.4.0esr-1
  • thunderbird Debian 14, Debian 13, Debian 12 1:91.4.0-1

debian advisories DEBIAN-CVE-2021-43541

  • firefox Ubuntu 18.04 LTS 95.0+build1-0ubuntu0.18.04.1
  • firefox Ubuntu 20.04 LTS 95.0+build1-0ubuntu0.20.04.1
  • firefox Ubuntu 22.04 LTS 95.0+build1-0ubuntu1
  • thunderbird Ubuntu 18.04 LTS 1:91.5.0+build1-0ubuntu0.18.04.1
  • thunderbird Ubuntu 20.04 LTS 1:91.5.0+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-43541

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 8 91.4.0-2.el8_5
  • thunderbird RHEL 7 91.4.0-3.el7_9
  • firefox RHEL 7 91.4.0-1.el7_9
  • firefox RHEL 8 91.4.0-1.el8_5
  • thunderbird RHEL 8.1 E4S 91.4.0-2.el8_1
  • thunderbird RHEL 8.2 EUS 91.4.0-2.el8_2
  • thunderbird RHEL 8.4 EUS 91.4.0-2.el8_4
  • firefox RHEL 8.1 E4S 91.4.0-1.el8_1

red hat advisories RHSA-2021:5055RHSA-2021:5047RHSA-2021:5048RHSA-2021:5045RHSA-2021:5046RHSA-2021:5017

  • MozillaThunderbird SLE Workstation Extension 15 SP3, SLE Workstation Extension 15 SP2 91.4.0-8.45.2
  • MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +11 more 91.4.0-112.83.1
  • MozillaFirefox SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +7 more 91.4.0-150.9.1
  • MozillaFirefox SLE Module for Desktop Applications 15 SP3, SLE Module for Desktop Applications 15 SP2 91.4.0-152.9.1
  • MozillaFirefox SLES 11 SP4-LTSS 91.4.0-78.154.1

suse advisories SUSE-SU-2021:4150-1SUSE-SU-2021:4000-1SUSE-SU-2021:3995-1SUSE-SU-2021:14859-1SUSE-SU-2021:3993-1

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 95.0-1.1
  • MozillaThunderbird openSUSE Tumbleweed 91.4.0-1.1
  • MozillaThunderbird openSUSE Leap 15.2 91.4.0-lp152.2.52.1
  • MozillaThunderbird openSUSE Leap 15.3 91.4.0-8.45.2
  • MozillaFirefox openSUSE Leap 15.2 91.4.0-lp152.2.74.1
  • MozillaFirefox openSUSE Leap 15.3 91.4.0-152.9.1

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:11669-1openSUSE-SU-2024:11670-1openSUSE-SU-2021:1635-1openSUSE-SU-2021:4150-1openSUSE-SU-2021:1575-1

  • thunderbird AlmaLinux 8 91.4.0-2.el8_5.alma
  • thunderbird AlmaLinux 8 91.4.0-2.el8_5.alma.plus
  • firefox AlmaLinux 8 91.4.0-1.el8_5.alma

almalinux advisories ALSA-2021:5045ALSA-2021:5013

  • thunderbird Rocky Linux 8 91.4.0-2.el8_5
  • firefox Rocky Linux 8 91.4.0-1.el8_5

rocky linux advisories RLSA-2021:5045RLSA-2021:5013

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 95.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 95.0-r0
  • firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +6 more 91.4.0-r0
  • thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 91.4.0-r0

alpine advisories ALPINE-CVE-2021-43541

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 95.0-1
  • thunderbird Arch Linux 91.4.0-1

arch linux advisories AVG-2606AVG-2608

Is CVE-2021-43541 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-2021-43541 updated cvss 6.1

Mozilla: External protocol handler parameters were unescaped

  • Red Hat Enterprise Linux 6 firefox, thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) firefox 91.4.0-1.el8_5, thunderbird 91.4.0-2.el8_5
    fixed: vendor fix RHSA-2021:5013
  • Red Hat Enterprise Linux AppStream E4S (v. 8.1) firefox 91.4.0-1.el8_1, thunderbird 91.4.0-2.el8_1
    fixed: vendor fix RHSA-2021:5017
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) firefox 91.4.0-1.el8_2, thunderbird 91.4.0-2.el8_2
    fixed: vendor fix RHSA-2021:5016
  • Red Hat Enterprise Linux AppStream EUS (v.8.4) firefox 91.4.0-1.el8_4, thunderbird 91.4.0-2.el8_4
    fixed: vendor fix RHSA-2021:5015
  • Red Hat Enterprise Linux Client (v. 7) firefox 91.4.0-1.el7_9, thunderbird 91.4.0-3.el7_9 Red Hat Enterprise Linux Client Optional (v. 7) firefox 91.4.0-1.el7_9 Red Hat Enterprise Linux Server (v. 7) firefox 91.4.0-1.el7_9 Red Hat Enterprise Linux Server Optional (v. 7) firefox 91.4.0-1.el7_9, thunderbird 91.4.0-3.el7_9 Red Hat Enterprise Linux Workstation (v. 7) firefox 91.4.0-1.el7_9, thunderbird 91.4.0-3.el7_9 Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 91.4.0-1.el7_9
    fixed: vendor fix RHSA-2021:5014

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

1.63% chance of exploitation in the next 30 days, higher than 76% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

  • Mozilla Thunderbird
  • Mozilla Firefox ESR
  • Mozilla Firefox

References

Sources

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.