Mastodon up to 4.2.23/4.3.10/4.4.2 Confirmation Email allocation of resources

Summaryinfo

A vulnerability classified as problematic has been found in Mastodon up to 4.2.23/4.3.10/4.4.2. Affected by this issue is some unknown functionality of the component Confirmation Email Handler. Performing a manipulation results in allocation of resources. This vulnerability is identified as CVE-2025-54879. The attack can be initiated remotely. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Mastodon up to 4.2.23/4.3.10/4.4.2. This affects some unknown processing of the component Confirmation Email 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. The summary by CVE is:

Mastodon is a free, open-source social network server based on ActivityPub Mastodon which facilitates LDAP configuration for authentication. In versions 3.1.5 through 4.2.24, 4.3.0 through 4.3.11 and 4.4.0 through 4.4.3, Mastodon's rate-limiting system has a critical configuration error where the email-based throttle for confirmation emails incorrectly checks the password reset path instead of the confirmation path, effectively disabling per-email limits for confirmation requests. This allows attackers to bypass rate limits by rotating IP addresses and send unlimited confirmation emails to any email address, as only a weak IP-based throttle (25 requests per 5 minutes) remains active. The vulnerability enables denial-of-service attacks that can overwhelm mail queues and facilitate user harassment through confirmation email spam. This is fixed in versions 4.2.24, 4.3.11 and 4.4.3.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2025-54879 since 07/31/2025. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 4.2.24, 4.3.11 or 4.4.3 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch e2592419d93fb41be03c2f3ff6a122fecb0e0952 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Name

• Mastodon

Version

• 4.2.0
• 4.2.1
• 4.2.2
• 4.2.3
• 4.2.4
• 4.2.5
• 4.2.6
• 4.2.7
• 4.2.8
• 4.2.9
• 4.2.10
• 4.2.11
• 4.2.12
• 4.2.13
• 4.2.14
• 4.2.15
• 4.2.16
• 4.2.17
• 4.2.18
• 4.2.19
• 4.2.20
• 4.2.21
• 4.2.22
• 4.2.23
• 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
• 4.4.0
• 4.4.1
• 4.4.2

License

• open-source

Website

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

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