CVE-2025-66482: Misskey has a login rate limit bypass via spoofed X-Forwarded-For header

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2025-12-16 · updated 2026-10-14
Weakness: CWE-307

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.

Affected products

misskey-dev misskey: from 13.1.0 before 2025.12.0; 13.0.0, 13.0.0-beta16, 13.0.0-beta21, 13.0.0-beta22, 13.0.0-beta23, 13.0.0-beta24 (+30) — fixed in 2025.12.0

How to fix

Upgrade to a fixed version: misskey-dev misskey 2025.12.0. Check the vendor advisory for mitigations.

References

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