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CVE-2026-46713 – ActivityPub Signature Spoofing (Improper Signature Verification) – Misskey 12.37.0

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Summary

CVE-2026-46713 is an improper cryptographic signature verification flaw (CWE-347) in Misskey, an open-source federated social media platform. A weakness in the way Misskey validates and compacts JSON-LD signatures allows spoofed ActivityPub activities to be accepted as valid, enabling unauthenticated attackers to forge federated activity. It is rated critical (CVSS 9.2).

Technical details

  • Root cause: A flaw in Misskey’s JSON-LD signature validation and compaction logic permits activities that should fail signature verification to be treated as legitimate.
  • Trigger conditions: An attacker sends crafted ActivityPub activities to an affected instance; the malformed JSON-LD payload passes signature checks despite being spoofed.
  • Attack vector: Network-based, low complexity, requiring no authentication and no user interaction.
  • Impact: High impact to integrity — attackers can inject forged activities that the server accepts as authentic, with downstream integrity consequences across federated data.

Affected software

  • Misskey versions 12.37.0 through 2026.5.3.

Severity

  • CVSS base score: 9.2 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:H/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade to Misskey 2026.5.4 or later, which contains the fix.
  • If no patch can be applied: There is no documented workaround; upgrading to the patched release is the only remediation. Where an immediate upgrade is not possible, restrict and monitor inbound federation traffic to the instance until the update is applied.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • The application-name meta tag’s content: Misskey

References

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How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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