Mastodon up to 4.3.16/4.4.10/4.5.3 insertion of sensitive information into sent data

Summaryinfo

A vulnerability identified as problematic has been detected in Mastodon up to 4.3.16/4.4.10/4.5.3. This affects an unknown function. The manipulation leads to insertion of sensitive information into sent data. This vulnerability is traded as CVE-2026-22246. It is possible to initiate the attack remotely. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Mastodon up to 4.3.16/4.4.10/4.5.3. This issue affects some unknown functionality. The manipulation with an unknown input leads to a insertion of sensitive information into sent data vulnerability. Using CWE to declare the problem leads to CWE-201. The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor. Impacted is confidentiality. The summary by CVE is:

Mastodon is a free, open-source social network server based on ActivityPub. Mastodon 4.3 added notifications of severed relationships, allowing end-users to inspect the relationships they lost as the result of a moderation action. The code allowing users to download lists of severed relationships for a particular event fails to check the owner of the list before returning the lost relationships. Any registered local user can access the list of lost followers and followed users caused by any severance event, and go through all severance events this way. The leaked information does not include the name of the account which has lost follows and followers. This has been fixed in Mastodon v4.3.17, v4.4.11 and v4.5.4.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-22246 since 01/07/2026. The exploitation is known to be easy. The attack may be initiated remotely. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1592 according to MITRE ATT&CK.

Upgrading to version 4.3.17, 4.4.11 or 4.5.4 eliminates this vulnerability.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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
• 4.4.0
• 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
• 4.5.0
• 4.5.1
• 4.5.2
• 4.5.3

Website

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

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