CVE-2021-21323

Name: CVE-2021-21323
Creator: NVD / NIST
Published: 2021-02-23T23:15:13.317+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 1.95%

Last modified Jun 17, 2026

CVE-2021-21323 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. Brave is an open source web browser with a focus on privacy and security. In Brave versions 1.17.73-1.20.103, the CNAME adblocking feature added in Brave 1.17.73 accidentally initiated DNS requests that bypassed the Brave Tor proxy. EPSS estimates a 1.95% chance of exploitation in the next 30 days.

Description

Brave is an open source web browser with a focus on privacy and security. In Brave versions 1.17.73-1.20.103, the CNAME adblocking feature added in Brave 1.17.73 accidentally initiated DNS requests that bypassed the Brave Tor proxy. Users with adblocking enabled would leak DNS requests from Tor windows to their DNS provider. (DNS requests that were not initiated by CNAME adblocking would go through Tor as expected.) This is fixed in Brave version 1.20.108

Metrics

CVSS 3.1

5.3/10

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

EPSS Probability

1.95%

77.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-200

Affected Software

Vendor	Product	Versions
Brave	Brave	>= 1.17.73, <= 1.20.103

References

https://github.com/brave/brave-browser/issues/13527Patch, Third Party Advisory
https://github.com/brave/brave-browser/security/advisories/GHSA-mqjf-9x5g-2rv6Third Party Advisory
https://github.com/brave/brave-core/commit/12fe321eaad8acc1cbd1d70b4128f687777bcf15Patch, Third Party Advisory
https://github.com/brave/brave-core/pull/7769Patch, Third Party Advisory
https://hackerone.com/reports/1077022Permissions Required, Third Party Advisory
https://github.com/brave/brave-browser/issues/13527Patch, Third Party Advisory
https://github.com/brave/brave-browser/security/advisories/GHSA-mqjf-9x5g-2rv6Third Party Advisory
https://github.com/brave/brave-core/commit/12fe321eaad8acc1cbd1d70b4128f687777bcf15Patch, Third Party Advisory
https://github.com/brave/brave-core/pull/7769Patch, Third Party Advisory
https://hackerone.com/reports/1077022Permissions Required, Third Party Advisory

Timeline

Published: Feb 23, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21323?

How severe is CVE-2021-21323?

CVE-2021-21323 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 1.95% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21323?

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-2021-21323?

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

Scan your code now

Source: NVD / NIST