# CVE-2026-41259: Mastodon: Insufficient verification of email addresses

> Attackers can bypass email domain restrictions during sign-up by using characters interpreted differently by mail servers, allowing unauthorized account creation.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Apr 2026
- **Updated:** 23 Apr 2026
- **Also known as:** BIT-mastodon-2026-41259, GHSA-5r37-qpwq-2jhh

## What is CVE-2026-41259?

CVE-2026-41259 is a high-severity vulnerability in mastodon, published on 23 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Mastodon is a free, open-source social network server based on ActivityPub. Prior to v4.5.9, v4.4.16, and v4.3.22, Mastodon allows restricting new user sign-up based on e-mail domain names, and performs basic validation on e-mail addresses, but fails to restrict characters that are interpreted differently by some mailing servers. This vulnerability is fixed in v4.5.9, v4.4.16, and v4.3.22.

Weakness: CWE-841 (Improper Enforcement of Behavioral Workflow)

## Which versions are affected by CVE-2026-41259?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mastodon` | Bitnami | All versions | 4.3.22, 4.4.16, 4.5.9 |

Products: Joinmastodon Mastodon.

## How do I fix CVE-2026-41259?

Upgrade mastodon to a fixed version for your release line: 4.3.22, 4.4.16 or 4.5.9.

## Is CVE-2026-41259 being exploited?

There is no known exploitation of CVE-2026-41259 in the wild and no public exploit code.

## Other vulnerabilities in mastodon

- [CVE-2023-36460](https://insights.sbomify.com/CVE-2023-36460/): Mastodon vulnerable to arbitrary file creation through media attachments (critical 10.0)
- [CVE-2022-2166](https://insights.sbomify.com/CVE-2022-2166/): Improper Restriction of Excessive Authentication Attempts in mastodon/mastodon (critical 9.8)
- [CVE-2022-24307](https://insights.sbomify.com/CVE-2022-24307/): Missing authorization in n/a (critical 9.8)
- [CVE-2018-21018](https://insights.sbomify.com/CVE-2018-21018/): Auth bypass in n/a (critical 9.8)
- [CVE-2024-23832](https://insights.sbomify.com/CVE-2024-23832/): Mastodon Remote user impersonation and takeover (critical 9.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-41259 and fix it if it is affected.

What it is: CVE-2026-41259 is a high-severity vulnerability in mastodon, published on 23 Apr 2026. 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-2026-41259 in the wild and no public exploit code.

Affected packages and fixed versions:
- mastodon (Bitnami): affected all versions; fixed in 4.3.22, 4.4.16, 4.5.9

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-2026-41259/ (Markdown: https://insights.sbomify.com/CVE-2026-41259/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-41259
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-41259
- OSV: https://osv.dev/vulnerability/CVE-2026-41259

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-41259/
Summaries are generated and may contain mistakes; the official description above is the record.