CVE-2021-23973

Name: CVE-2021-23973
Creator: NVD / NIST
Published: 2021-02-26T02:15:13.243+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 1.38%

Last modified Jun 17, 2026

CVE-2021-23973 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. When trying to load a cross-origin resource in an audio/video context a decoding error may have resulted, and the content of that error may have revealed information about the resource. This vulnerability affects Firefox < 86, Thunderbird < 78.8, and Firefox ESR < 78.8.. EPSS estimates a 1.38% chance of exploitation in the next 30 days.

Description

When trying to load a cross-origin resource in an audio/video context a decoding error may have resulted, and the content of that error may have revealed information about the resource. This vulnerability affects Firefox < 86, Thunderbird < 78.8, and Firefox ESR < 78.8.

Metrics

CVSS 3.1

6.5/10

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

EPSS Probability

1.38%

68.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-209

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 86.0
Mozilla	Firefox Esr	< 78.8
Mozilla	Thunderbird	< 78.8
Debian	Debian Linux	9.0
Debian	Debian Linux	10.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1690976Issue Tracking, Permissions Required, Vendor Advisory
https://lists.debian.org/debian-lts-announce/2021/03/msg00000.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202104-09Third Party Advisory
https://security.gentoo.org/glsa/202104-10Third Party Advisory
https://www.debian.org/security/2021/dsa-4866Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-07/Release Notes, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-08/Release Notes, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-09/Release Notes, Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1690976Issue Tracking, Permissions Required, Vendor Advisory
https://lists.debian.org/debian-lts-announce/2021/03/msg00000.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202104-09Third Party Advisory
https://security.gentoo.org/glsa/202104-10Third Party Advisory
https://www.debian.org/security/2021/dsa-4866Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-07/Release Notes, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-08/Release Notes, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-09/Release Notes, Vendor Advisory

Timeline

Published: Feb 26, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-23973?

How severe is CVE-2021-23973?

CVE-2021-23973 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 1.38% probability of exploitation in the next 30 days.

How do I fix CVE-2021-23973?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-23973?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST