# CVE-2021-32707: Bypass of image blocking in Nextcloud Mail

> Attackers can bypass image blocking in Nextcloud Mail via CSS background images, potentially revealing user read status.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/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:** Not needed
- **Fix available:** No
- **Published:** 12 Jul 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-xxp4-44xc-8crh

## What is CVE-2021-32707?

CVE-2021-32707 is a medium-severity vulnerability in nextcloud security-advisories, published on 12 Jul 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Nextcloud Mail is a mail app for Nextcloud. In versions prior to 1.9.6, the Nextcloud Mail application does not, by default, render images in emails to not leak the read state. The privacy filter failed to filter images with a `background-image` CSS attribute. Note that the images were still passed through the Nextcloud image proxy, and thus there was no IP leakage. The issue was patched in version 1.9.6 and 1.10.0. No workarounds are known to exist.

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

## Which versions are affected by CVE-2021-32707?

It affects 1 product.


Products: Nextcloud Mail.

## How do I fix CVE-2021-32707?

No fix has been published for CVE-2021-32707 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-32707 being exploited?

There is no known exploitation of CVE-2021-32707 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-2021-32707 and fix it if it is affected.

What it is: CVE-2021-32707 is a medium-severity vulnerability in nextcloud security-advisories, published on 12 Jul 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-32707 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-2021-32707/ (Markdown: https://insights.sbomify.com/CVE-2021-32707/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32707
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32707
- OSV: https://osv.dev/vulnerability/CVE-2021-32707

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32707/
Summaries are generated and may contain mistakes; the official description above is the record.