# CVE-2021-21323: Regression in DNS leakage from Tor windows

> Brave browser users with adblocking enabled leak DNS requests from Tor windows, exposing browsing activity to DNS providers.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 23 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-mqjf-9x5g-2rv6

## What is CVE-2021-21323?

CVE-2021-21323 is a medium-severity vulnerability in brave-browser, published on 23 Feb 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2021-21323?

It affects 1 product.


Products: Brave Brave.

## How do I fix CVE-2021-21323?

No fix has been published for CVE-2021-21323 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21323 being exploited?

There is no known exploitation of CVE-2021-21323 in the wild and no public exploit code.

## Other vulnerabilities in brave-browser

- [CVE-2021-45884](https://insights.sbomify.com/CVE-2021-45884/): Information disclosure in n/a (high 7.5)
- [CVE-2022-47932](https://insights.sbomify.com/CVE-2022-47932/): Denial of service in n/a (medium 6.5)
- [CVE-2022-47933](https://insights.sbomify.com/CVE-2022-47933/): Denial of service in n/a (medium 6.5)
- [CVE-2022-47934](https://insights.sbomify.com/CVE-2022-47934/): Denial of service in n/a (medium 6.5)
- [CVE-2018-10798](https://insights.sbomify.com/CVE-2018-10798/): Denial of service in n/a (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21323 and fix it if it is affected.

What it is: CVE-2021-21323 is a medium-severity vulnerability in brave-browser, published on 23 Feb 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-21323 in the wild and no public exploit code.

Affected product: brave-browser. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-21323/ (Markdown: https://insights.sbomify.com/CVE-2021-21323/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21323
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21323
- OSV: https://osv.dev/vulnerability/CVE-2021-21323

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21323/
Summaries are generated and may contain mistakes; the official description above is the record.