CVE-2026-72916: Mastodon: SSRF Protection Bypass via IPv4-compatible IPv6 Addresses

Published Aug 10, 2026
·
Updated

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.privateaddress? in app/lib/privateaddresscheck.rb normalized IPv4-mapped IPv6 addresses but did not recognize IPv4-compatible IPv6 addresses with IPAddr#ipv4compat?. An attacker could supply an address in the omitted range to bypass the ALLOWEDPRIVATEADDRESSES 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.

Affected Software

1 affected component
Mastodon Mastodon<4.4.21, <4.5.14, <4.6.4, <4.7.0-beta.1

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade Mastodon to a version that resolves this vulnerability.

    Fixed in 4.4.21
  2. Upgrade

    Upgrade Mastodon to a version that resolves this vulnerability.

    Fixed in 4.5.14
  3. Upgrade

    Upgrade Mastodon to a version that resolves this vulnerability.

    Fixed in 4.6.4
  4. Upgrade

    Upgrade Mastodon to a version that resolves this vulnerability.

    Fixed in 4.7.0-beta.1

Event History

Aug 10, 2026
CVE Published
via MITRE·09:19 PM
Data Sourced
via MITRE·09:19 PM
DescriptionWeakness
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Frequently Asked Questions

1

What is the severity of CVE-2026-72916?

CVE-2026-72916 has a risk rating of 47, indicating a significant security vulnerability.

2

What type of vulnerability is CVE-2026-72916?

CVE-2026-72916 is classified as a Server-Side Request Forgery (SSRF) vulnerability.

3

How do I fix CVE-2026-72916?

To address CVE-2026-72916, upgrade Mastodon to the latest versions 4.4.21, 4.5.14, 4.6.4, or 4.7.0-beta.1 or later.

4

Who is affected by CVE-2026-72916?

All users running versions of Mastodon prior to 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1 are affected by CVE-2026-72916.

5

What does CVE-2026-72916 exploit?

CVE-2026-72916 exploits a flaw in Mastodon that allows the bypass of SSRF protection through IPv4-compatible IPv6 addresses.

Company

Resources

Contact

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CVE-2026-72916 - Mastodon: SSRF Protection Bypass via IPv4-compatible IPv6 Addresses - SecAlerts