Mastodon up to 4.3.17/4.4.11/4.5.4 API allocation of resources

Summaryinfo

A vulnerability categorized as problematic has been discovered in Mastodon up to 4.3.17/4.4.11/4.5.4. The impacted element is an unknown function of the component API Handler. The manipulation results in allocation of resources. This vulnerability is cataloged as CVE-2026-23963. The attack may be launched remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Mastodon up to 4.3.17/4.4.11/4.5.4. It has been classified as problematic. Affected is an unknown functionality of the component API Handler. The manipulation with an unknown input leads to a allocation of resources vulnerability. CWE is classifying the issue as CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. This is going to have an impact on availability. CVE summarizes:

Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.5, 4.4.12, and 4.3.18, the server does not enforce a maximum length for the names of lists or filters, or for filter keywords, allowing any user to set an arbitrarily long string as the name or keyword. Any local user can abuse the list or filter fields to cause disproportionate storage and computing resource usage. They can additionally cause their own web interface to be unusable, although they must intentionally do this to themselves or unknowingly approve a malicious API client. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-23963 since 01/19/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

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.

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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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