CVE-2026-72916
Published:August 10, 2026
Updated:August 31, 2026
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.
Affected Packages
https://github.com/mastodon/mastodon.git (GITHUB):
Affected version(s) >=v4.5.0 <v4.5.14Fix Suggestion:
Update to version v4.5.14https://github.com/mastodon/mastodon.git (GITHUB):
Affected version(s) >=v0.1.0 <v4.4.21Fix Suggestion:
Update to version v4.4.21https://github.com/mastodon/mastodon.git (GITHUB):
Affected version(s) >=v4.6.0 <v4.6.4Fix Suggestion:
Update to version v4.6.4Related Resources (11)
Do you need more information?
Contact UsCVSS v4
Base Score:
6.3
Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
NONE
Subsequent System Confidentiality
LOW
Subsequent System Integrity
LOW
Subsequent System Availability
LOW
CVSS v3
Base Score:
6.5
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
LOW
Weakness Type (CWE)
EPSS
Base Score:
0.36