# CVE-2026-41259: CVE-2026-41259

Status: published. Published: 2026-04-23. Updated: 2026-11-11.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- joinmastodon / mastodon: < 4.3.22 (affected, custom). Source: NVD
- joinmastodon / mastodon: ≥ 4.4.0; < 4.4.16 (affected, custom). Source: NVD
- joinmastodon / mastodon: ≥ 4.5.0; < 4.5.9 (affected, custom). Source: NVD

## NVD configuration conditions

Affected CPE matches depend on the following AND/OR and negation conditions:

```json
[
  {
    "negate": false,
    "nodes": [
      {
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "4.3.22",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "4.4.16",
            "versionStartIncluding": "4.4.0",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "4.5.9",
            "versionStartIncluding": "4.5.0",
            "vulnerable": true
          }
        ],
        "negate": false,
        "operator": "OR"
      }
    ],
    "operator": "OR"
  }
]
```

## Severity and prioritization

- CVSS 4.0: 8.2 (high); 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: security-advisories@github.com

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N; source: NVD: nvd@nist.gov

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: exploitation none; automatable yes; technical impact partial; source NVD SSVC: 134c704f-9b21-4f2e-91b3-4a467353bcc0

- Weaknesses: CWE-841

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/mastodon/mastodon/security/advisories/GHSA-5r37-qpwq-2jhh (security-advisories@github.com; Vendor Advisory)

## Provenance

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-41259; retrieved 2026-11-12; source updated 2026-11-11

Revision: 2a89f18d049eb7158dc5e17a73ef558211aead54aa498135eebbf6a21d2f957e

Canonical: https://y2.dev/cve/CVE-2026-41259

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.