Race Condition Affecting firefox-esr package, versions <91.4.0esr-1


Severity

Recommended
0.0
medium
0
10

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Threat Intelligence

EPSS
1.16% (63rd percentile)

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  • Snyk IDSNYK-ECHOLATEST-FIREFOXESR-18169304
  • published22 Jul 2026
  • disclosed8 Dec 2021

Introduced: 8 Dec 2021

CVE-2021-43538  (opens in a new tab)
CWE-362  (opens in a new tab)

How to fix?

Upgrade Echo:latest firefox-esr to version 91.4.0esr-1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream firefox-esr package and not the firefox-esr package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

By misusing a race in our notification code, an attacker could have forcefully hidden the notification for pages that had received full screen and pointer lock access, which could have been used for spoofing attacks. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

CVSS Base Scores

version 3.1