# CVE-2021-22915: Security feature bypass in Nextcloud Server

> Attackers can bypass brute-force protection by exploiting IPv6 subnet handling, allowing unlimited login attempts against Nextcloud servers.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 11 Jun 2021
- **Updated:** 3 Aug 2024

## What is CVE-2021-22915?

CVE-2021-22915 is a critical vulnerability in Fedoraproject Fedora, published on 11 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Nextcloud server before 19.0.11, 20.0.10, 21.0.2 is vulnerable to brute force attacks due to lack of inclusion of IPv6 subnets in rate-limiting considerations. This could potentially result in an attacker bypassing rate-limit controls such as the Nextcloud brute-force protection.

Weakness: CWE-307 (Improper Restriction of Excessive Authentication Attempts)

## Which versions are affected by CVE-2021-22915?

It affects 2 products.


Products: Fedoraproject Fedora, Nextcloud Nextcloud Server.

## How do I fix CVE-2021-22915?

No fix has been published for CVE-2021-22915 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-22915 being exploited?

There is no known exploitation of CVE-2021-22915 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-22915 and fix it if it is affected.

What it is: CVE-2021-22915 is a critical vulnerability in Fedoraproject Fedora, published on 11 Jun 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-2021-22915 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2021-22915/ (Markdown: https://insights.sbomify.com/CVE-2021-22915/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-22915
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-22915
- OSV: https://osv.dev/vulnerability/CVE-2021-22915

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-22915/
Summaries are generated and may contain mistakes; the official description above is the record.