CVE-2026-47389 Mastodon: SSRF protection bypass on older Ruby versions
Attackers can bypass SSRF protections on older Ruby versions to access internal network resources and cloud metadata endpoints.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-47389?
CVE-2026-47389 is a high-severity server-side request forgery vulnerability in mastodon, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-47389?
1 open source package ship an affected version, including mastodon.
| Package | Affected | Fixed in |
|---|---|---|
mastodon Bitnami | From 4.5.0 | 4.5.10 |
How do I fix CVE-2026-47389?
Upgrade mastodon to 4.5.10 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-47389 being exploited?
There is no known exploitation of CVE-2026-47389 in the wild and no public exploit code.
Sources
Also known as BIT-mastodon-2026-47389, GHSA-xx55-4rrg-8xg6.