CVE-2025-66482

When using an untrusted reverse proxy or not using a reverse proxy at all, attackers 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, making it still vulnerable if the configuration is not set correctly.

Workaround

If you are running Misskey with a trusted reverse proxy, you should not be affected by this vulnerability.

• There is no workaround for the Misskey itself. Please update Misskey to the latest version or set up a trusted reverse proxy.
• From v2025.9.1 to v2025.11.1, workaround is available. Set trustProxy: false in config file.
• This is patched in v2025.12.0 by flipping default value of trustProxy to false. If you are using trusted reverse proxy and not remember you manually overrided this value, please take time to check your config for optimal behavior.

Details

Fastify recommend not trusting X-Forwarded-For IPs
Due to misconfiguration in https://github.com/misskey-dev/misskey/blob/develop/packages/backend/src/server/api/SigninApiService.ts#L94 attacks can spoof their IPs.

PoC

POST /api/signin-flow HTTP/1.1
Host: misskey.localhost:3123
Content-Length: 45
Content-Type: application/json
Connection: keep-alive
X-Forwarded-For: 127.1.1.31, 1.1.1.12

{"username":"admin",
	"password":"password"}

An attacker can brute force accounts bypassing rate limiting protection.

CVE-2025-66482 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2025.12.0-alpha.2); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-66482? CVE-2025-66482 is a medium-severity security vulnerability in misskey-js (npm), affecting versions >= 2025.9.1, < 2025.12.0-alpha.2. It is fixed in 2025.12.0-alpha.2.
2. How severe is CVE-2025-66482? CVE-2025-66482 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of misskey-js are affected by CVE-2025-66482? misskey-js (npm) versions >= 2025.9.1, < 2025.12.0-alpha.2 is affected.
4. Is there a fix for CVE-2025-66482? Yes. CVE-2025-66482 is fixed in 2025.12.0-alpha.2. Upgrade to this version or later.
5. Is CVE-2025-66482 exploitable, and should I be worried? Whether CVE-2025-66482 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-66482 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-66482? Upgrade misskey-js to 2025.12.0-alpha.2 or later.