Mastodon up to 4.3.17/4.4.11/4.5.4 Web Push Subscription Update Endpoint authorization

Summaryinfo

A vulnerability has been found in Mastodon up to 4.3.17/4.4.11/4.5.4 and classified as critical. Affected is an unknown function of the component Web Push Subscription Update Endpoint. The manipulation leads to authorization. This vulnerability is referenced as CVE-2026-23964. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Mastodon up to 4.3.17/4.4.11/4.5.4 and classified as critical. This issue affects an unknown part of the component Web Push Subscription Update Endpoint. 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 confidentiality, integrity, and availability. The summary by CVE is:

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, an insecure direct object reference in the web push subscription update endpoint lets any authenticated user update another user's push subscription by guessing or obtaining the numeric subscription id. This can be used to disrupt push notifications for other users and also leaks the web push subscription endpoint. Any user with a web push subscription is impacted, because another authenticated user can tamper with their push subscription settings if they can guess or obtain the subscription id. This allows an attacker to disrupt push notifications by changing the policy (whether to filter notifications from non-followers or non-followed users) and subscribed notification types of their victims. Additionally, the endpoint returns the subscription object, which includes the push notification endpoint for this subscription, but not its keypair. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-23964 since 01/19/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not 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.

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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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