CVE-2026-47746Network attack vector

Unauthenticated forged activity acceptance via mutable JSON-LD contexts

Published Aug 3, 2026 · Updated Aug 3, 2026

TOCTOU in Misskey 12.37.0 through 2026.5.3 allows remote attackers to submit fraudulent ActivityPub activities that pass validation. InboxProcessorService re-fetched mutable JSON-LD contexts between signature verification and compaction, allowing the two operations to interpret different data. No account or user interaction is required; a forged activity is accepted as authentic, corrupting federated data integrity.

CVSS severity9.2
Critical
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

TOCTOU in Misskey 12.37.0 through 2026.5.3 allows remote attackers to submit fraudulent ActivityPub activities that pass validation. InboxProcessorService re-fetched mutable JSON-LD contexts between signature verification and compaction, allowing the two operations to interpret different data. No account or user interaction is required; a forged activity is accepted as authentic, corrupting federated data integrity.

The record

CVE
CVE-2026-47746
Published
Aug 3, 2026
Updated
Aug 3, 2026
Vendor
Misskey Project
Product
Misskey
Classifications
CWE-367, CAPEC-29, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 12.37.0, < 2026.5.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Misskey Project · Misskeyversion=>= 12.37.0, < 2026.5.4

Published CVSS scores

9.2GitHub Security AdvisoryCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:H/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
CAPEC-29Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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