CVE Intelligence
Medium Authentication exploit reference

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

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.

Published Dec 15, 2025 · Updated Oct 14, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: GitHub_M

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.3% (30-day exploitation probability)+4
  • Technical severity (medium)+3
  • CISA SSVC: exploitation "poc"+5
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.34%
ahead of 26% of scored CVEs · Oct 14, 2026
Affects
Misskey
Misskey and 1 more
CVSS base
6.5
Medium · 4 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Proof of concept
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — github.com (NIST National Vulnerability Database)
  • Npm Misskey-js: fixed in version 2025.12.0-alpha.2 — github.com (GitHub Security Advisories)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Misskey Misskey, Misskey-dev Misskey, Npm Misskey-js).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. Search available logs for exploit probes matching the vulnerability class (authentication), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Misskey Misskey version 13.0.0-rc11version 13.0.0-beta37version 13.0.0-beta38version 13.0.0-beta39version 13.0.0-beta40version 13.0.0-beta41version 13.0.0-beta42version 13.0.0-beta43
and 29 more version 13.0.0-rc1version 13.0.0-rc10version 13.0.0version 13.0.0-rc2version 13.0.0-rc3version 13.0.0-rc4version 13.0.0-rc5version 13.0.0-rc6version 13.0.0-rc7version 13.0.0-rc8version 13.0.0-rc9version 13.0.0-beta35≥ 13.1.0 and < 2025.12.0version 13.0.0-beta16version 13.0.0-beta21version 13.0.0-beta22version 13.0.0-beta23version 13.0.0-beta24version 13.0.0-beta25version 13.0.0-beta26version 13.0.0-beta27version 13.0.0-beta28version 13.0.0-beta29version 13.0.0-beta30version 13.0.0-beta31version 13.0.0-beta32version 13.0.0-beta33version 13.0.0-beta34version 13.0.0-beta36
Vulnerable NIST National Vulnerability Database
Misskey-dev Misskey version >= 2025.9.1, < 2025.12.0-alpha.2 Vulnerable CVE Program (cve.org) e CISA ADP
Npm Misskey-js ≥ 2025.9.1 and < 2025.12.0-alpha.2 Vulnerable GitHub Security Advisories

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
Low

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
6.9 CVSS 4.0 Medium — — security-advisories@github.com via NIST National Vulnerability Database
6.9 CVSS 4.0 Medium — — GitHub_M via CVE Program (cve.org) e CISA ADP
6.5 CVSS 3.1 Medium 3.9 2.5 nvd@nist.gov via NIST National Vulnerability Database
6.5 CVSS 3.1 Medium — — GitHub, Inc. via GitHub Security Advisories
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-307 · Improper Restriction of Excessive Authentication Attempts

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.34%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Review authentication logs: logins without MFA, anomalous sessions and recently created accounts.
web/proxy/WAF logsnetwork IDS/IPSauthentication logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • Fix documented
    Oct 14, 2026 · GitHub Security Advisories
  • Affected products added · npm/misskey-js
    Oct 14, 2026 · GitHub Security Advisories
  • Affected products added · misskey-dev/misskey
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 6.5
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • 2025
  • CVE published
    Dec 15, 2025 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

  • 1× References added · Oct 14, 2026 – Oct 14, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

4 on the record

Elsewhere on this site

Misskey
every CVE for this vendor
Authentication
same class
CWE-307
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-104817 Misskey: Lack of rate limiting and size restrictions in RSS fetching API 2d
  • CVE-2026-104816 Misskey: Cross-site scripting in RSS feed item links 2d
  • CVE-2026-103937 Misskey: Denial of service resulting from insufficient cleanup processing during file uploads 2d
  • CVE-2026-48115 Misskey: Improper Authorization in the Announcements API Aug 3, 2026
  • CVE-2026-46713 Misskey: JSON-LD signature validation + compaction may lead to improper activity handling Aug 3, 2026
  • CVE-2026-47746 Misskey: JSON-LD signature validation + compaction is vulnerable to timing attacks Aug 3, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2025-66482 is "Misskey has a login rate limit bypass via spoofed X-Forwarded-For header", rated Medium. It affects Misskey (Misskey); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.5 describes technical severity. EPSS 0.34% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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