CVE-2026-41259

publishedCWE-841

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.

Technical severity8.2 highCVSS 4.0 · NVD: [email protected]

Published2026-04-23Source updated 2026-11-11

Collected2026-11-121 attributed source

Fixes and workarounds

No remediation reported in collected sources.

Missing remediation information is not evidence that no patch exists.

Affected products and versions

Affected products, source version ranges and reporting authorities
Product	Versions	Authority
mastodon joinmastodon	< 4.3.22 (affected, custom)	NVD
mastodon joinmastodon	≥ 4.4.0; < 4.4.16 (affected, custom)	NVD
mastodon joinmastodon	≥ 4.5.0; < 4.5.9 (affected, custom)	NVD

Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.

NVD applicability configurations (1)

These expressions retain AND/OR operators, negation, and required environmental products. A listed product is not sufficient to establish exposure when additional conditions apply.

[
  {
    "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"
  }
]

CVSS assessments

CVSS scores, vectors and reporting authorities
Version / score	Vector	Authority
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`	NVD: [email protected]
3.1 / 7.5 high	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`	NVD: [email protected]

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[email protected] · Vendor Advisory

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