CVE-2021-43541

MEDIUM 6.5CVE-2021-43541 · Published 08/12/2021 · updated 17/06/2026

In short

CVE-2021-43541 is a MEDIUM (CVSS 6.5) vulnerability affecting firefox (mozilla), firefox esr (mozilla), thunderbird (mozilla).
Chance of exploitation in the next 30 days (EPSS): 1.7%, higher than 77.2% of all vulnerabilities.
Fix: update to 95.0, 91.4.0 or later.

Package	Affected versions	Patched versions
firefox mozilla	`< 95.0`	`95.0`
firefox esr mozilla	`< 91.4.0`	`91.4.0`
thunderbird mozilla	`< 91.4.0`	`91.4.0`

Description

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.

References

bugzilla.mozilla.org/show_bug.cgi · Issue Tracking
lists.debian.org/debian-lts-announce/2021/12/msg00030.html · Mailing List
lists.debian.org/debian-lts-announce/2022/01/msg00001.html · Mailing List
security.gentoo.org/glsa/202202-03 · Third Party Advisory
security.gentoo.org/glsa/202208-14 · Third Party Advisory
debian.org/security/2021/dsa-5026 · Third Party Advisory
debian.org/security/2022/dsa-5034 · Third Party Advisory
mozilla.org/security/advisories/mfsa2021-52 · Vendor Advisory
mozilla.org/security/advisories/mfsa2021-53 · Vendor Advisory
mozilla.org/security/advisories/mfsa2021-54 · Vendor Advisory

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Package

Affected versions

Patched versions

firefox

mozilla

< 95.0

95.0

firefox esr

mozilla

< 91.4.0

91.4.0

thunderbird

mozilla

< 91.4.0

91.4.0

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