CVE-2021-43543

6.1 MEDIUM 1% exploit odds Fix listed

What it is

Documents loaded with the CSP sandbox directive could have escaped the sandbox's script restriction by embedding additional content. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

At a glance

Exploitability: Can be exploited over the network without logging in, but needs a user to act. Limited direct impact.
Exploit odds: 1.5% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2021-12-08 22:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-06-17 04:11 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 1.5% in the next 30 days (EPSS).
Severity: 6.1 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2021-12-08 22:15 UTC
Last modified: 2026-06-17 04:11 UTC
Exploit probability: 1.5% · EPSS, next 30 days
Weakness: CWE-79 · Cross-site scripting
Record status: Modified

Affected

Mozilla Firefox < 95.0
Mozilla Firefox Esr < 91.4.0
Mozilla Thunderbird < 91.4.0
Debian Linux 9.0
Debian Linux 10.0
Debian Linux 11.0

Attack profile CVSS 3.1 · 6.1

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-43543.md and follow it. Check whether this project is affected by CVE-2021-43543. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record