Which versions of Misskey are affected by CVE-2026-47746?

A JSON-LD signature validation flaw in Misskey's federation layer allows remote attackers to inject fraudulent activities that bypass integrity checks and propagate across federated networks.. A patch is available.

How to fix or mitigate CVE-2026-47746?

Within 24 hours, identify all self-hosted Misskey deployments and confirm versions running 12.37.0-2026.5.3 against your inventory. Within 7 days, implement enhanced federated peer verification, enable comprehensive audit logging of all ActivityPub activities and message processing, and implement network-level rate limiting on federation traffic. Within 30 days, establish automated daily monitoring of Misskey vendor advisories for patch release, conduct forensic review of federation logs for exploitation indicators, and prepare upgrade procedures for immediate deployment once a patch becomes available.

Misskey CVE-2026-47746

Q: What is the CVSS score of CVE-2026-47746?

CVE-2026-47746 has a CVSS 4.0 base score of 8.9 (High). CVSS 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.2%.

EUVD-2026-52488 HIGH

Time-of-check Time-of-use (TOCTOU) Race Condition (CWE-367)

2026-08-03 GitHub_M

Information Disclosure Misskey Misskey Dev

8.9

CVSS 4.0 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

8.9 HIGH

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

vuln.today AI

6.8 MEDIUM

Network vector and no auth required; AC:H reflects non-trivial JSON-LD context manipulation; S:C because fraudulent activities can propagate to downstream federated instances beyond the vulnerable component.

3.1 AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N

4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Patch available

Aug 03, 2026 - 23:02 EUVD

Source Code Evidence Fetched

Aug 03, 2026 - 22:32 vuln.today

Analysis Generated

Aug 03, 2026 - 22:32 vuln.today

CVE Published

Aug 03, 2026 - 21:56 cve.org

HIGH 8.9

DescriptionCVE.org

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.

AnalysisAI

JSON-LD signature validation in Misskey's ActivityPub federation layer accepts fraudulent federated activities due to a TOCTOU flaw where the JSON-LD parsing context used during signature verification is not shared with the context used during subsequent message processing. Affected are all self-hosted Misskey instances running versions 12.37.0 through 2026.5.3. A remote, unauthenticated attacker operating or spoofing a federated server can craft payloads that pass signature checks yet resolve to malicious content during processing, resulting in high integrity impact across the instance and potentially propagating to federated peers; no public exploit or CISA KEV listing has been identified at time of analysis.

Technical ContextAI

Misskey implements the ActivityPub protocol for federation, which relies on JSON-LD (Linked Data) for structured message signing via JSON-LD signatures. JSON-LD documents are compacted and expanded using a 'context' that governs term resolution and data interpretation. The root cause (CWE-367: Time-of-Check Time-of-Use Race Condition) is an architectural gap: the JSON-LD context is not shared between the signature verification phase and the subsequent compaction/processing phase. Because the two phases may resolve the same document under different contexts, an attacker can embed content that passes cryptographic verification under one interpretation but is processed as different, attacker-controlled content under another. This is a classic TOCTOU flaw applied to a cryptographic trust boundary. The affected CPE is cpe:2.3:a:misskey-dev:misskey:*:*:*:*:*:*:*:*, covering the version range 12.37.0 up to (but not including) 2026.5.4.

RemediationAI

Upgrade to Misskey version 2026.5.4, which is confirmed as the fix release by the vendor security advisory GHSA-38jx-423m-g387 (https://github.com/misskey-dev/misskey/security/advisories/GHSA-38jx-423m-g387) and the official release at https://github.com/misskey-dev/misskey/releases/tag/2026.5.4. If an immediate upgrade is not feasible, restricting federation to a known-trusted allowlist of instances is the most actionable compensating control - this limits the attack surface to servers you control or vet, though it degrades interoperability with the broader Fediverse. Disabling federation entirely eliminates exposure but removes the core federated functionality of the platform. No configuration-level workaround fully addresses the TOCTOU architectural issue without the patch. Upstream fix availability is confirmed via the tagged release; no earlier patched version is indicated.