Which versions of Misskey are affected by CVE-2026-46713?

A critical signature validation flaw in Misskey versions 12.37.0 through 2026.5.3 allows unauthenticated attackers to forge authenticated ActivityPub activities, enabling impersonation of users and…. A patch is available.

How to fix or mitigate CVE-2026-46713?

Within 24 hours, isolate affected Misskey instances from federated networks and disable all ActivityPub federation with external peers; prepare a complete inventory of Misskey deployments noting versions 12.37.0-2026.5.3. Within 7 days, implement deep inspection logging of ActivityPub activities to detect signature validation anomalies, engage Misskey project maintainers for patch timeline estimates, and brief stakeholders on the integrity risk to federated communications. Within 30 days, establish a patch deployment plan contingent on vendor release; if no patch emerges by day 30, evaluate migration to alternative federated platforms or implement application-layer cryptographic signature verification as a compensating control before re-enabling federation.

Misskey CVE-2026-46713

Q: What is the CVSS score of CVE-2026-46713?

CVE-2026-46713 has a CVSS 4.0 base score of 9.2 (Critical). CVSS 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/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-2026-52485 CRITICAL

Improper Verification of Cryptographic Signature (CWE-347)

2026-08-03 GitHub_M

Information Disclosure Jwt Attack Misskey

9.2

CVSS 4.0 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

9.2 CRITICAL

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/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

9.3 CRITICAL

Remote unauthenticated signature bypass with no user interaction gives AV:N/AC:L/PR:N/UI:N; forged activities affect other federated actors/instances so S:C with I:H, limited C:L, and no availability impact.

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

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/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

Low

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 - 21:37 cve.org

CRITICAL 9.2

DescriptionCVE.org

Misskey is an open source, federated social media platform. Versions 12.37.0 and later, but prior to 2026.5.4, contain a vulnerability in the JSON-LD signature validation and compaction process that allows spoofed activities to be accepted as valid. This issue has been fixed in version 2026.5.4.

AnalysisAI

Signature validation bypass in Misskey (versions 12.37.0 through prior to 2026.5.4) allows an attacker to have spoofed ActivityPub activities accepted as authentic. The flaw resides in the JSON-LD signature validation and compaction logic (CWE-347), enabling forgery of federated actions such as posts or actions attributed to other actors/instances. The CVSS 4.0 base score is 9.2 (Critical) with a network, unauthenticated, low-complexity vector emphasizing integrity impact; no public exploit has been identified at time of analysis, and it is not listed in CISA KEV.

Technical ContextAI

Misskey is an open-source, federated (fediverse) social media server that speaks the ActivityPub protocol. In ActivityPub federation, remote servers authenticate the origin and integrity of incoming activities using cryptographic signatures, and JSON-LD documents are 'compacted'/normalized before the signature is verified. This CVE is a CWE-347 (Improper Verification of Cryptographic Signature) weakness in that JSON-LD signature validation and compaction pipeline: discrepancies between what is signed and what is processed after compaction allow a forged document to pass verification. The affected component is identified by CPE cpe:2.3:a:misskey-dev:misskey covering all versions in the vulnerable range. The 'Jwt Attack' tag is likely a loose categorization of the signature-forgery class rather than literal JWT usage, since ActivityPub relies on Linked Data / HTTP signatures rather than JWTs.

RemediationAI

Vendor-released patch: upgrade to Misskey 2026.5.4, which bundles fixes for this issue (GHSA-w8x2-gpq6-jxvf / CVE-2026-46713) alongside four other advisories addressed in the same release. Follow the upgrade instructions in the release notes at https://github.com/misskey-dev/misskey/releases/tag/2026.5.4 and review the advisory at https://github.com/misskey-dev/misskey/security/advisories/GHSA-w8x2-gpq6-jxvf. If immediate upgrade is not possible, meaningful compensating controls are limited because the flaw is in core federation processing; operators can reduce exposure by restricting or pausing federation with untrusted or unknown remote instances (using Misskey's instance blocking/allow-list or moving to a more restrictive federation policy), accepting the trade-off that this breaks legitimate interaction with those servers, and by monitoring for anomalous or impersonated activities from remote actors. These are stopgaps only - patching to 2026.5.4 is the reliable fix.