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Vulnerability record · CVE-2026-41259 · published 23 April 2026

CVE-2026-41259: Joinmastodon mastodon vulnerability

Joinmastodon · Mastodon

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.

8.2 CVSS 4.0 High EPSS 0.37% · top 72.2% CWE-841 · CWE-841
8.2CVSS 4.0 base score
0.37%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References
17 Jun 2026Last modified by NVD

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.

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:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/mastodon/mastodon/security/advisories/GHSA-5r37-qpwq-2jhh Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.9CVE-2023-36460Joinmastodon mastodon path traversal vulnerabilityMastodon is a free, open-source social network server based on ActivityPub. Starting in version 3.5.0 and prior to versions 3.5.9, 4.0.5, and 4.1.3, …EPSS 40%9.8CVE-2024-23832Joinmastodon mastodon authentication bypass by spoofing vulnerabilityMastodon is a free, open-source social network server based on ActivityPub Mastodon allows configuration of LDAP for authentication. Due to insuffici…EPSS 2.5%9.8CVE-2022-2166Joinmastodon mastodon improper restriction of authentication attempts vulnerabilityImproper Restriction of Excessive Authentication Attempts in GitHub repository mastodon/mastodon prior to 4.0.0.EPSS 1.1%9.8CVE-2022-24307Joinmastodon mastodon incorrect authorization vulnerabilityMastodon before 3.3.2 and 3.4.x before 3.4.6 has incorrect access control because it does not compact incoming signed JSON-LD activities. (JSON-LD si…EPSS 1.4%9.8CVE-2018-21018Joinmastodon mastodon insufficient session expiration vulnerabilityMastodon before 2.6.3 mishandles timeouts of incompletely established sessions.EPSS 2.6%8.2CVE-2024-37903Joinmastodon mastodon missing authorization vulnerabilityMastodon is a self-hosted, federated microblogging platform. Starting in version 2.6.0 and prior to versions 4.1.18 and 4.2.10, by crafting specific …EPSS 0.53%7.7CVE-2024-25623Joinmastodon mastodon unrestricted file upload vulnerabilityMastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.2.7, 4.1.15, 4.0.15, and 3.5.19, when fetching remote…EPSS 0.52%7.5CVE-2026-23962Joinmastodon mastodon allocation without limits vulnerabilityMastodon is a free, open-source social network server based on ActivityPub. Mastodon versions before v4.3.18, v4.4.12, and v4.5.5 do not have a limit…EPSS 0.55%

Source: NIST National Vulnerability Database (record CVE-2026-41259), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.