CVE-2026-47389
HighCVSS 8.6Exploitation Probability (EPSS)
Low risk14th percentile — higher than 14% of all known CVEs
Summary
Mastodon prior to versions 4.5.10, 4.4.17, and 4.3.23 has a vulnerability that allows incorrect recognition of IPv4-mapped IPv6 addresses, potentially leading to TCP connections to private IPv4 addresses. Attackers can exploit this vulnerability by publishing appropriate DNS records.
Risk Assessment
Organizations may be exposed to unauthorized access to local resources or data, leading to serious security incidents. In particular, attackers may gain access to addresses such as 127.0.0.1, creating a risk of data leakage.
Recommendation
It is recommended to update Mastodon to versions 4.5.10, 4.4.17, or 4.3.23 to eliminate this vulnerability. Additionally, it is advisable to monitor and secure DNS configurations to prevent the publication of unauthorized records.
Original NVD description (English source)
Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.5.10, 4.4.17, and 4.3.23, when using Ruby versions older than 3.4, PrivateAddressCheck.private_address? returns false for IPv4-mapped IPv6 addresses (::ffff:a.b.c.d) corresponding to some private IPv4 addresses, depending on Ruby version, this can include loopback, RFC1918 private networks, and link-local space. An attacker who controls DNS for any domain can publish an AAAA record with such a mapped address; any outbound HTTP fetch Mastodon performs against that hostname then opens a real TCP connection to the underlying IPv4 address, including 127.0.0.1 and cloud-metadata endpoints such as 169.254.169.254. This vulnerability is fixed in 4.5.10, 4.4.17, and 4.3.23.