Mastodon up to 4.3.17/4.4.11/4.5.4 authorization

Summaryinfo

A vulnerability classified as problematic was found in Mastodon up to 4.3.17/4.4.11/4.5.4. The impacted element is an unknown function. Such manipulation leads to authorization. This vulnerability is uniquely identified as CVE-2026-23961. The attack can be launched remotely. No exploit exists. Upgrading the affected component is advised.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Mastodon up to 4.3.17/4.4.11/4.5.4. Affected by this issue is an unknown function. The manipulation with an unknown input leads to a authorization vulnerability. Using CWE to declare the problem leads to CWE-863. The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions. Impacted is integrity. CVE summarizes:

Mastodon is a free, open-source social network server based on ActivityPub. Mastodon allows server administrators to suspend remote users to prevent interactions. However, some logic errors allow already-known posts from such suspended users to appear in timelines if boosted. Furthermore, under certain circumstances, previously-unknown posts from suspended users can be processed. This issue allows old posts from suspended users to occasionally end up on timelines on all Mastodon versions. Additionally, on Mastodon versions from v4.5.0 to v4.5.4, v4.4.5 to v4.4.11, v4.3.13 to v4.3.17, and v4.2.26 to v4.2.29, remote suspended users can partially bypass the suspension to get new posts in. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-23961 since 01/19/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available.

Upgrading to version 4.3.18, 4.4.12 or 4.5.5 eliminates this vulnerability. The upgrade is hosted for download at github.com.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-4207). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Name

• Mastodon

Version

• 4.3.0
• 4.3.1
• 4.3.2
• 4.3.3
• 4.3.4
• 4.3.5
• 4.3.6
• 4.3.7
• 4.3.8
• 4.3.9
• 4.3.10
• 4.3.11
• 4.3.12
• 4.3.13
• 4.3.14
• 4.3.15
• 4.3.16
• 4.3.17
• 4.4.0
• 4.4.1
• 4.4.2
• 4.4.3
• 4.4.4
• 4.4.5
• 4.4.6
• 4.4.7
• 4.4.8
• 4.4.9
• 4.4.10
• 4.4.11
• 4.5.0
• 4.5.1
• 4.5.2
• 4.5.3
• 4.5.4

Website

• Product: https://github.com/mastodon/mastodon/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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