CVE-2020-26953

4.3 MEDIUM 1% exploit odds Fix listed

What it is

It was possible to cause the browser to enter fullscreen mode without displaying the security UI; thus making it possible to attempt a phishing attack or otherwise confuse the user. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

At a glance

Exploitability: Can be exploited over the network without logging in, but needs a user to act. Limited direct impact.
Exploit odds: 1.3% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2020-12-09 01:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-06-17 03:08 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 1.3% in the next 30 days (EPSS).
Severity: 4.3 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2020-12-09 01:15 UTC
Last modified: 2026-06-17 03:08 UTC
Exploit probability: 1.3% · EPSS, next 30 days
Weakness: CWE-1021
Record status: Modified

Affected

Mozilla Firefox < 83.0
Mozilla Firefox Esr < 78.5
Mozilla Thunderbird < 78.5

Attack profile CVSS 3.1 · 4.3

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

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/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-2020-26953.md and follow it. Check whether this project is affected by CVE-2020-26953. 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