---
id: CVE-2026-72916
title: 'Mastodon is a free, open-source social network server based on ActivityPub'
summary: >-
  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 …
severity: none
cwe:
  - CWE-918
  - CWE-1286
published: '2026-08-10'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T20:55:04.493'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-72916'
references:
  - url: >-
      https://github.com/mastodon/mastodon/commit/18c61f286f1f5718a8f517940ba384866ffa3892
    label: security-advisories@github.com
  - url: >-
      https://github.com/mastodon/mastodon/commit/467c933459c7d0e5513475b9e4888afaedfb1074
    label: security-advisories@github.com
  - url: >-
      https://github.com/mastodon/mastodon/commit/930aa9fee26bf9eaefe27826fa1061288d83373b
    label: security-advisories@github.com
  - url: >-
      https://github.com/mastodon/mastodon/commit/da47a1bd3cd07935d7ca55a1f4f1a76f7f167e0d
    label: security-advisories@github.com
  - url: 'https://github.com/mastodon/mastodon/releases/tag/v4.4.21'
    label: security-advisories@github.com
  - url: 'https://github.com/mastodon/mastodon/releases/tag/v4.5.14'
    label: security-advisories@github.com
  - url: 'https://github.com/mastodon/mastodon/releases/tag/v4.6.4'
    label: security-advisories@github.com
  - url: 'https://github.com/mastodon/mastodon/releases/tag/v4.7.0-beta.1'
    label: security-advisories@github.com
  - url: >-
      https://github.com/mastodon/mastodon/security/advisories/GHSA-vwhj-3g83-v276
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.00586
epssPercentile: 0.45734
ingestedAt: '2026-09-09T21:22:45.526Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.