CVE-2021-43542

Mozilla: XMLHttpRequest error codes could have leaked the existence of an external protocol handler

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Severity

Moderate

Red Hat Product Security

6.1

CVSS 3.0

Review impact separately from score.

Published · December 7, 2021

Updated · November 22, 2025

Description

Using XMLHttpRequest, an attacker could have identified installed applications by probing error messages for loading external protocols. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

CVSS score applicability

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation

No mitigation is specified in collected source.

CVSS / CWE

CVSS 3.0 · 6.1
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CWE-209 · Generation of Error Message Containing Sensitive Information