CVE-2021-43536

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-12-08 · updated 2026-06-17
Weakness: CWE-200

Description

Under certain circumstances, asynchronous functions could have caused a navigation to fail but expose the target URL. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

Affected products

Debian Linux: 9.0, 10.0, 11.0
Mozilla Firefox: before 95.0 — fixed in 95.0
Mozilla Firefox ESR: before 91.4.0 — fixed in 91.4.0
Mozilla Thunderbird: before 91.4.0 — fixed in 91.4.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 95.0; Mozilla Firefox ESR 91.4.0; Mozilla Thunderbird 91.4.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1730120
https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
https://security.gentoo.org/glsa/202202-03
https://security.gentoo.org/glsa/202208-14
https://www.debian.org/security/2021/dsa-5026
https://www.debian.org/security/2022/dsa-5034
https://www.mozilla.org/security/advisories/mfsa2021-52/
https://www.mozilla.org/security/advisories/mfsa2021-53/
https://www.mozilla.org/security/advisories/mfsa2021-54/
https://bugzilla.mozilla.org/show_bug.cgi?id=1730120
https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html

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