# CVE-2021-26036: [20210702] - Core - DoS through usergroup table manipulation

> Attackers can cause a denial of service in Joomla by manipulating the usergroups table due to missing input validation.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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:** Not needed
- **Fix available:** No
- **Published:** 7 Jul 2021
- **Updated:** 25 Feb 2026
- **Also known as:** BIT-joomla-2021-26036, GHSA-g983-3grj-v7qw

## What is CVE-2021-26036?

CVE-2021-26036 is a high-severity denial of service vulnerability in Joomla Joomla\!, published on 7 Jul 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered in Joomla! 2.5.0 through 3.9.27. Missing validation of input could lead to a broken usergroups table.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2021-26036?

1 open source package ship an affected version, including joomla. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `joomla` | Bitnami | From 2.5.0 to 3.9.27 | None |

Products: Joomla Joomla\!.

## How do I fix CVE-2021-26036?

No fix has been published for CVE-2021-26036 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-26036 being exploited?

There is no known exploitation of CVE-2021-26036 in the wild and no public exploit code.

## Other vulnerabilities in Joomla Joomla\!

- [CVE-2016-10033](https://insights.sbomify.com/CVE-2016-10033/): PHPMailer Command Injection (critical 9.8, exploited in the wild)
- [CVE-2023-23752](https://insights.sbomify.com/CVE-2023-23752/): Joomla! Improper Access Control (medium 5.3, exploited in the wild)
- [CVE-2026-48902](https://insights.sbomify.com/CVE-2026-48902/): Joomla! Core - [20260518] - Transport encryption downgrade for password and username reset links (critical 9.8)
- [CVE-2025-25226](https://insights.sbomify.com/CVE-2025-25226/): [20250401] - Joomla Framework - SQL injection vulnerability in quoteNameStr method of Database package (critical 9.8)
- [CVE-2022-23795](https://insights.sbomify.com/CVE-2022-23795/): [20220303] - Core - User row are not bound to a authentication mechanism (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-26036 and fix it if it is affected.

What it is: CVE-2021-26036 is a high-severity denial of service vulnerability in Joomla Joomla\!, published on 7 Jul 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-2021-26036 in the wild and no public exploit code.

Affected packages and fixed versions:
- joomla (Bitnami): affected from 2.5.0 up to 3.9.27; no fix listed

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-2021-26036/ (Markdown: https://insights.sbomify.com/CVE-2021-26036/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-26036
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-26036
- OSV: https://osv.dev/vulnerability/CVE-2021-26036

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-26036/
Summaries are generated and may contain mistakes; the official description above is the record.