# CVE-2021-39220: Bypass of image blocking in Nextcloud Mail

> Attackers can bypass image blocking in Nextcloud Mail to leak user IP addresses and read state via relative protocol images.

- **Severity:** Low 3.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 25 Oct 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-6q9v-wm8r-rcv5

## What is CVE-2021-39220?

CVE-2021-39220 is a low-severity vulnerability in nextcloud security-advisories, published on 25 Oct 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Nextcloud is an open-source, self-hosted productivity platform The Nextcloud Mail application prior to versions 1.10.4 and 1.11.0 does by default not render images in emails to not leak the read state or user IP. The privacy filter failed to filter images with a relative protocol. It is recommended that the Nextcloud Mail application is upgraded to 1.10.4 or 1.11.0. There are no known workarounds aside from upgrading.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2021-39220?

It affects 1 product.


Products: Nextcloud Mail.

## How do I fix CVE-2021-39220?

No fix has been published for CVE-2021-39220 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-39220 being exploited?

There is no known exploitation of CVE-2021-39220 in the wild and no public exploit code.

## Other vulnerabilities in nextcloud security-advisories

- [CVE-2021-32652](https://insights.sbomify.com/CVE-2021-32652/): Missing permission check on email metadata retrieval (high 8.8)
- [CVE-2022-31132](https://insights.sbomify.com/CVE-2022-31132/): Unauthenticated SSRF in 3rd party module "cerdic/csstidy" (high 8.3)
- [CVE-2024-52508](https://insights.sbomify.com/CVE-2024-52508/): Nextcloud Mail auto configurator can be tricked into sending account information to wrong servers (high 8.2)
- [CVE-2023-23943](https://insights.sbomify.com/CVE-2023-23943/): Blind SSRF via server URL input in the Nextcloud Mail app (medium 5.0)
- [CVE-2023-45660](https://insights.sbomify.com/CVE-2023-45660/): Require strict cookies for image proxy requests in Nextcloud Mail (medium 4.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-39220 and fix it if it is affected.

What it is: CVE-2021-39220 is a low-severity vulnerability in nextcloud security-advisories, published on 25 Oct 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-39220 in the wild and no public exploit code.

Affected product: nextcloud security-advisories. 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-2021-39220/ (Markdown: https://insights.sbomify.com/CVE-2021-39220/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-39220
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-39220
- OSV: https://osv.dev/vulnerability/CVE-2021-39220

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-39220/
Summaries are generated and may contain mistakes; the official description above is the record.