mastodon up to 4.2.28/4.3.16/4.4.10/4.5.3 Outbound Request server-side request forgery

Summaryinfo

A vulnerability was found in mastodon up to 4.2.28/4.3.16/4.4.10/4.5.3. It has been classified as critical. This issue affects some unknown processing of the component Outbound Request Handler. This manipulation causes server-side request forgery. This vulnerability is registered as CVE-2026-22245. Remote exploitation of the attack is possible. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in mastodon up to 4.2.28/4.3.16/4.4.10/4.5.3. It has been declared as critical. Affected by this vulnerability is an unknown code block of the component Outbound Request Handler. The manipulation with an unknown input leads to a server-side request forgery vulnerability. The CWE definition for the vulnerability is CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Mastodon is a free, open-source social network server based on ActivityPub. By nature, Mastodon performs a lot of outbound requests to user-provided domains. Mastodon, however, has some protection mechanism to disallow requests to local IP addresses (unless specified in `ALLOWED_PRIVATE_ADDRESSES`) to avoid the "confused deputy" problem. The list of disallowed IP address ranges was lacking some IP address ranges that can be used to reach local IP addresses. An attacker can use an IP address in the affected ranges to make Mastodon perform HTTP requests against loopback or local network hosts, potentially allowing access to otherwise private resources and services. This is fixed in Mastodon v4.5.4, v4.4.11, v4.3.17 and v4.2.29.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-22245 since 01/07/2026. The exploitation appears to be easy. The attack can be launched remotely. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 4.2.29, 4.3.17, 4.4.11 or 4.5.4 eliminates this vulnerability.

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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
• 4.2.24
• 4.2.25
• 4.2.26
• 4.2.27
• 4.2.28
• 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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