# CVE-2021-34823: XML external entity in n/a

> An XXE vulnerability in the ON24 ScreenShare plugin allows remote attackers to read local files via a crafted HTTP request.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Aug 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-ff42-ccp4-hwcv

## What is CVE-2021-34823?

CVE-2021-34823 is a critical vulnerability in n/a, published on 13 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The ON24 ScreenShare (aka DesktopScreenShare.app) plugin before 2.0 for macOS allows remote file access via its built-in HTTP server. This allows unauthenticated remote users to retrieve files accessible to the logged-on macOS user. When a remote user sends a crafted HTTP request to the server, it triggers a code path that will download a configuration file from a specified remote machine over HTTP. There is an XXE flaw in processing of this configuration file that allows reading local (to macOS) files and uploading them to remote machines.

Weakness: CWE-611 (Improper Restriction of XML External Entity Reference)

## Which versions are affected by CVE-2021-34823?

It affects 1 product.


Products: On24 Screenshare.

## How do I fix CVE-2021-34823?

No fix has been published for CVE-2021-34823 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-34823 being exploited?

There is no known exploitation of CVE-2021-34823 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34823 and fix it if it is affected.

What it is: CVE-2021-34823 is a critical vulnerability in n/a, published on 13 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-34823 in the wild and no public exploit code.

Affected product: n/a. 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-2021-34823/ (Markdown: https://insights.sbomify.com/CVE-2021-34823/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34823
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34823
- OSV: https://osv.dev/vulnerability/CVE-2021-34823

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34823/
Summaries are generated and may contain mistakes; the official description above is the record.