CVE-2021-43541

MEDIUMNVD 6.56.5—

6.5

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.

CVSS v3: 6.5
EG Score: 6.5(medium)
EPSS: 58.2%
KEV: Not listed

Published

December 8, 2021

Last Modified

November 21, 2024

References (20)

security@mozillahttps://bugzilla.mozilla.org/show_bug.cgi?id=1696685
security@mozillahttps://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
security@mozillahttps://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
security@mozillahttps://security.gentoo.org/glsa/202202-03
security@mozillahttps://security.gentoo.org/glsa/202208-14
security@mozillahttps://www.debian.org/security/2021/dsa-5026
security@mozillahttps://www.debian.org/security/2022/dsa-5034
security@mozillahttps://www.mozilla.org/security/advisories/mfsa2021-52/
security@mozillahttps://www.mozilla.org/security/advisories/mfsa2021-53/
security@mozillahttps://www.mozilla.org/security/advisories/mfsa2021-54/
af854a3a-2127-422b-91ae-364da2661108https://bugzilla.mozilla.org/show_bug.cgi?id=1696685
af854a3a-2127-422b-91ae-364da2661108https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
af854a3a-2127-422b-91ae-364da2661108https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
af854a3a-2127-422b-91ae-364da2661108https://security.gentoo.org/glsa/202202-03
af854a3a-2127-422b-91ae-364da2661108https://security.gentoo.org/glsa/202208-14

Patch Availability(13)

Vendor / Ecosystem	Fixed in / Patch	Released	Source
ubuntu	thunderbird-locale-id (1:91.5.0+build1-0ubuntu0.21.10.1) @ impish	2026-05-26	ubuntu
ubuntu	thunderbird-locale-id (1:91.5.0+build1-0ubuntu0.20.04.1) @ focal	2026-05-26	ubuntu
ubuntu	firefox-locale-ast (95.0+build1-0ubuntu0.21.10.1) @ impish	2026-05-26	ubuntu
redhat	thunderbird-0:91.4.0-2.el8_1	2021-12-09	redhat
redhat	thunderbird-0:91.4.0-2.el8_2	2021-12-09	redhat
redhat	thunderbird-0:91.4.0-3.el7_9	2021-12-09	redhat
redhat	thunderbird-0:91.4.0-2.el8_4	2021-12-09	redhat
redhat	thunderbird-0:91.4.0-2.el8_5	2021-12-09	redhat
redhat	firefox-0:91.4.0-1.el8_1	2021-12-08	redhat
redhat	firefox-0:91.4.0-1.el8_2	2021-12-08	redhat
redhat	firefox-0:91.4.0-1.el8_5	2021-12-08	redhat
redhat	firefox-0:91.4.0-1.el8_4	2021-12-08	redhat
redhat	firefox-0:91.4.0-1.el7_9	2021-12-08	redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

All Vendor Advisories

(13)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 11× in last 7d / 20× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

2026-06-08 14:15 UTCEPSS rescore
2026-06-08 14:15 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore
2026-06-05 06:09 UTCEPSS rescore
2026-06-05 06:09 UTCEPSS rescore
2026-06-04 13:10 UTCEPSS rescore
2026-06-04 13:10 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-05-31 22:29 UTCEPSS rescore
2026-05-31 22:29 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore
2026-05-29 13:42 UTCEPSS rescore

Frequently asked(5)

What is CVE-2021-43541?

CVE-2021-43541 is a medium vulnerability published on December 8, 2021. 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.

When was CVE-2021-43541 disclosed?

CVE-2021-43541 was first published in the National Vulnerability Database on December 8, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-43541 actively exploited?

CVE-2021-43541 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 58.2% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-43541?

CVE-2021-43541 has a CVSS v3 base score of 6.5 (NVD).

How do I remediate CVE-2021-43541?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-43541, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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