CVE-2026-72916

Description

Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1, PrivateAddressCheck.private_address? in app/lib/private_address_check.rb normalized IPv4-mapped IPv6 addresses but did not recognize IPv4-compatible IPv6 addresses with IPAddr#ipv4_compat?. An attacker could supply an address in the omitted range to bypass the ALLOWED_PRIVATE_ADDRESSES protection and make Mastodon send HTTP requests to loopback interfaces, potentially accessing private resources and services. Exploitation requires a system that supports the obsolete IPv4-compatible IPv6 mechanism. This issue is fixed in versions 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1.

References

• https://github.com/mastodon/mastodon/commit/18c61f286f1f5718a8f517940ba384866ffa3892
• https://github.com/mastodon/mastodon/commit/467c933459c7d0e5513475b9e4888afaedfb1074
• https://github.com/mastodon/mastodon/commit/930aa9fee26bf9eaefe27826fa1061288d83373b
• https://github.com/mastodon/mastodon/commit/da47a1bd3cd07935d7ca55a1f4f1a76f7f167e0d
• https://github.com/mastodon/mastodon/releases/tag/v4.4.21