CVE Catalog

CVE-2026-22245

High
Published: Translated: NVD NIST

Summary

Mastodon, a free, open-source social network server based on ActivityPub, has a vulnerability in its protection mechanism that blocks requests to local IP addresses. Some IP address ranges are missing, allowing an attacker to make Mastodon perform HTTP requests against loopback or local network hosts, potentially accessing private resources and services. This is fixed in Mastodon v4.5.4, v4.4.11, v4.3.17 and v4.2.29.

Risk Assessment

The risk includes the possibility of using Mastodon as a 'confused deputy' to attack internal services, which could lead to disclosure of sensitive data or unauthorized access to network resources.

Recommendation

It is recommended to immediately update Mastodon to one of the patched versions (v4.5.4, v4.4.11, v4.3.17, or v4.2.29) to eliminate the vulnerability.

Other vulnerabilities in Mastodon

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Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS