Server-Side Request Forgery (SSRF) in Mastodon - CVE-2026-47389
Published: May 23, 2026
Vulnerability identifier: #VU132180
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:L/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-47389
CWE-ID: CWE-918
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Mastodon
Affected software:
Mastodon
Mastodon
Detailed vulnerability description
The vulnerability allows a remote attacker to disclose sensitive information via server-side request forgery.
The vulnerability exists due to incomplete list of disallowed inputs in PrivateAddressCheck.private_address? when processing hostnames that resolve to IPv4-mapped IPv6 addresses. A remote attacker can publish a crafted AAAA record for a domain they control to disclose sensitive information via server-side request forgery.
On affected Ruby versions, outbound HTTP fetches can reach loopback, private network, link-local, and cloud metadata addresses through such mapped addresses.
How to mitigate CVE-2026-47389
Install security update from vendor's website.