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CVE-2025-66482 — misskey-js

Fix: misskey-dev/misskey@5512898

CVE-2025-66482 is a CWE-307 vulnerability in misskey-js. A fix is available for misskey-js — see the affected versions and patch details below.

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

Also known asGHSA-wwrj-3hvj-prpm
Published
Dec 15, 2025
Updated
Aug 12, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Sep 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-66482.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs27th percentile — riskier than 27% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

1other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
misskey-jsnpm
765downloads / week

Description

Summary

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"}

image

Impact

An attacker can brute force accounts bypassing rate limiting protection.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmmisskey-js≥ 2025.9.1&&< 2025.12.0-alpha.22025.12.0-alpha.2npm install misskey-js@2025.12.0-alpha.2

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for misskey-js, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update misskey-js to 2025.12.0-alpha.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66482 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-66482 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2025-66482. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

### Summary 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
O3 Security · Impact-Aware SCA

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O3 Security finds CVE-2025-66482 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

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CVE-2025-66482: misskey-js | O3 Security