Origin validation error in Mastodon - #VU165891
Published: November 11, 2026
Vulnerability identifier: #VU165891
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-346
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass IP blocks and some built-in rate limits in Mastodon.
The vulnerability exists due to improper validation of client IP address information in Mastodon's recommended nginx.conf configuration when handling HTTP requests containing client-controlled headers. A remote attacker can supply an arbitrary IP address through an HTTP request header to spoof their source address and evade these restrictions.
Affected software
Mastodon
Remediation
Install security update from vendor's website.
Mastodon - update to 4.7.5