Misskey has a login rate limit bypass via spoofed X-Forwarded-For header

Vulnerability Description

Misskey is an open source, federated social media platform. Attackers who use an untrusted reverse proxy or not using a reverse proxy at all can bypass IP rate limiting by adding a forged X-Forwarded-For header. Starting with version 2025.9.1, an option (`trustProxy`) has been added in config file to prevent this from happening. However, it is initialized with an insecure default value before version 2025.12.0-alpha.2, making it still vulnerable if the configuration is not set correctly. This is patched in v2025.12.0-alpha.2 by flipping default value of `trustProxy` to `false`. Users of a trusted reverse proxy who are unsure if they manually overode this value should check their config for optimal behavior. Users are running Misskey with a trusted reverse proxy should not be affected by this vulnerability. From v2025.9.1 to v2025.11.1, workaround is available. Set `trustProxy: false` in config file.

References

• https://github.com/misskey-dev/misskey/security/advisories/GHSA-wwrj-3hvj-prpm
• https://github.com/misskey-dev/misskey/commit/5512898463fa8487b9e6488912f35102b91f25f7