# CVE-2021-36093: DoS attack using PostMaster filters

> Attackers can cause a denial of service by sending emails that get stuck in PostMaster filters, affecting OTRS ticket system administrators.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 Sep 2021
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-p8h5-xqwr-ww86, UBUNTU-CVE-2021-36093

## What is CVE-2021-36093?

CVE-2021-36093 is a medium-severity denial of service vulnerability in Otrs Otrs, published on 6 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

It's possible to create an email which can be stuck while being processed by PostMaster filters, causing DoS. 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 7.0.28 and prior versions; 8.0.x version 8.0.15 and prior versions.

Weakness: CWE-185 (Incorrect Regular Expression)

## Which versions are affected by CVE-2021-36093?

It affects 1 product.


Products: Otrs Otrs.

## How do I fix CVE-2021-36093?

No fix has been published for CVE-2021-36093 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-36093 being exploited?

There is no known exploitation of CVE-2021-36093 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-2021-36093 and fix it if it is affected.

What it is: CVE-2021-36093 is a medium-severity denial of service vulnerability in Otrs Otrs, published on 6 Sep 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-2021-36093 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-2021-36093/ (Markdown: https://insights.sbomify.com/CVE-2021-36093/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-36093
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-36093
- OSV: https://osv.dev/vulnerability/CVE-2021-36093

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-36093/
Summaries are generated and may contain mistakes; the official description above is the record.