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Vulnerability record · CVE-2018-21018 · published 22 September 2019

CVE-2018-21018: Joinmastodon mastodon insufficient session expiration vulnerability

Joinmastodon · Mastodon

Mastodon before 2.6.3 mishandles timeouts of incompletely established sessions.

9.8 CVSS 3.1 Critical EPSS 2.6% · top 15.5% CWE-613 · Insufficient session expiration
9.8CVSS 3.1 base score, v2 7.5
2.6%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
8References
17 Jun 2026Last modified by NVD

Description

Mastodon before 2.6.3 mishandles timeouts of incompletely established sessions.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

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

References

LinkTags
https://github.com/tootsuite/mastodon/pull/9329 PatchThird Party Advisory
https://github.com/tootsuite/mastodon/pull/9381 PatchThird Party Advisory
https://github.com/tootsuite/mastodon/releases/tag/v2.6.2 Release NotesThird Party Advisory
https://github.com/tootsuite/mastodon/releases/tag/v2.6.3 Release NotesThird Party Advisory
https://github.com/tootsuite/mastodon/pull/9329 PatchThird Party Advisory
https://github.com/tootsuite/mastodon/pull/9381 PatchThird Party Advisory
https://github.com/tootsuite/mastodon/releases/tag/v2.6.2 Release NotesThird Party Advisory
https://github.com/tootsuite/mastodon/releases/tag/v2.6.3 Release NotesThird Party 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%8.2CVE-2026-41259Joinmastodon mastodon vulnerabilityMastodon 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 us…EPSS 0.37%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 0.51%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-2018-21018), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.