# CVE-2021-21439: Possible DoS attack using a special crafted URL in email body

> Attackers can cause high CPU usage or system halts in OTRS by sending emails with specially crafted URLs in the body.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **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:** Yes
- **Published:** 14 Jun 2021
- **Updated:** 16 Sep 2024
- **Also known as:** DEBIAN-CVE-2021-21439, GHSA-58p7-gj75-3437, UBUNTU-CVE-2021-21439

## What is CVE-2021-21439?

CVE-2021-21439 is a medium-severity denial of service vulnerability in Otrs Otrs, published on 14 Jun 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

DoS attack can be performed when an email contains specially designed URL in the body. It can lead to the high CPU usage and cause low quality of service, or in extreme case bring the system to a halt. This issue affects: OTRS AG ((OTRS)) Community Edition 6.0.x version 6.0.1 and later versions. OTRS AG OTRS 7.0.x version 7.0.26 and prior versions; 8.0.x version 8.0.13 and prior versions.

Weakness: CWE-755 (Improper Handling of Exceptional Conditions), CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2021-21439?

It affects 1 product.


Products: Otrs Otrs.

## How do I fix CVE-2021-21439?

Upgrade to a fixed version.

## Is CVE-2021-21439 being exploited?

There is no known exploitation of CVE-2021-21439 in the wild and no public exploit code.

## Other vulnerabilities in Otrs Otrs

- [CVE-2026-48188](https://insights.sbomify.com/CVE-2026-48188/): SQL Injection via MySQL Quote Method (critical 9.1)
- [CVE-2013-4717](https://insights.sbomify.com/CVE-2013-4717/): SQL injection in n/a (high 8.8)
- [CVE-2017-14635](https://insights.sbomify.com/CVE-2017-14635/): Code injection in n/a (high 8.8)
- [CVE-2023-5422](https://insights.sbomify.com/CVE-2023-5422/): SSL Certificates are not checked for E-Mail Handling (high 8.7)
- [CVE-2023-6254](https://insights.sbomify.com/CVE-2023-6254/): Password is send back to client (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21439 and fix it if it is affected.

What it is: CVE-2021-21439 is a medium-severity denial of service vulnerability in Otrs Otrs, published on 14 Jun 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-2021-21439 in the wild and no public exploit code.

Affected product: Otrs Otrs. 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-2021-21439/ (Markdown: https://insights.sbomify.com/CVE-2021-21439/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21439
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21439
- OSV: https://osv.dev/vulnerability/CVE-2021-21439

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21439/
Summaries are generated and may contain mistakes; the official description above is the record.