Mastodon up to 4.4.20/4.5.13/4.6.3 PrivateAddressCheck private_address_check.rb PrivateAddressCheck.private_address? infinite loop

Summaryinfo

A vulnerability marked as critical has been reported in Mastodon up to 4.4.20/4.5.13/4.6.3. This affects the function PrivateAddressCheck.private_address? of the file app/lib/private_address_check.rb of the component PrivateAddressCheck. The manipulation leads to infinite loop. This vulnerability is listed as CVE-2026-72916. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability was found in Mastodon up to 4.4.20/4.5.13/4.6.3 and classified as critical. This issue affects the function PrivateAddressCheck.private_address? of the file app/lib/private_address_check.rb of the component PrivateAddressCheck. The manipulation with an unknown input leads to a infinite loop vulnerability. Using CWE to declare the problem leads to CWE-835. The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-72916 since 08/10/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 4.4.21, 4.5.14, 4.6.4 or 4.7.0-beta.1 eliminates this vulnerability.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Name

• Mastodon

Version

• 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
• 4.4.11
• 4.4.12
• 4.4.13
• 4.4.14
• 4.4.15
• 4.4.16
• 4.4.17
• 4.4.18
• 4.4.19
• 4.4.20
• 4.5.0
• 4.5.1
• 4.5.2
• 4.5.3
• 4.5.4
• 4.5.5
• 4.5.6
• 4.5.7
• 4.5.8
• 4.5.9
• 4.5.10
• 4.5.11
• 4.5.12
• 4.5.13
• 4.6.0
• 4.6.1
• 4.6.2
• 4.6.3

Website

• Product: https://github.com/mastodon/mastodon/

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