CVE-2026-46713 Overview
CVE-2026-46713 is a signature verification vulnerability [CWE-347] in Misskey, an open source federated social media platform. The flaw resides in the JSON-LD signature validation and compaction process. Attackers can craft spoofed ActivityPub activities that Misskey accepts as valid, undermining the integrity of federated communications. The vulnerability affects Misskey versions 12.37.0 through releases prior to 2026.5.4. The maintainers have patched the issue in version 2026.5.4.
Critical Impact
Remote unauthenticated attackers can forge federated activities and impersonate other actors across the fediverse, compromising the integrity of posts, follows, and moderation actions.
Affected Products
- Misskey versions 12.37.0 and later
- Misskey versions prior to 2026.5.4
- Federated Misskey instances participating in ActivityPub
Discovery Timeline
- 2026-08-03 - CVE-2026-46713 published to NVD
- 2026-08-04 - Last updated in NVD database
Technical Details for CVE-2026-46713
Vulnerability Analysis
Misskey federates with other ActivityPub servers by exchanging JSON-LD documents signed by the originating actor. The receiving server must canonicalize (compact) the JSON-LD and verify the attached Linked Data Signature against the actor's public key. In vulnerable versions, the compaction and signature verification steps do not agree on which fields are covered by the signature. An attacker can inject additional properties or reorder context terms so that the compacted payload differs from what the signature actually authenticates. Misskey treats the payload as verified even though critical fields were never signed by the claimed actor.
The issue is classified under [CWE-347: Improper Verification of Cryptographic Signature]. Because the platform trusts spoofed activities, an attacker can inject content attributed to arbitrary remote users on any vulnerable instance that federates with them.
Root Cause
The root cause is a mismatch between JSON-LD compaction and signature validation. Fields present in the incoming activity are consumed by application logic even when they fall outside the signed portion of the document. The signature verification routine returns success on the reduced view of the document, while downstream handlers act on the full, unverified view.
Attack Vector
Exploitation requires only network access to a vulnerable Misskey instance. The attacker sends a crafted ActivityPub payload, such as a Create, Follow, Announce, or Delete activity, to the target's inbox. The payload carries a valid signature bound to attacker-controlled fields, plus additional unsigned fields that Misskey processes as if signed by the impersonated actor. No user interaction and no authentication are required.
No verified public exploit code is available at this time. Refer to the GitHub Security Advisory GHSA-w8x2-gpq6-jxvf for maintainer-published technical details.
Detection Methods for CVE-2026-46713
Indicators of Compromise
- Inbound ActivityPub POST requests to /inbox or /users/*/inbox containing JSON-LD documents with duplicated or unusual @context entries.
- Federated activities whose actor field points to a remote instance but whose signature.creator key does not match the actor's published key ID.
- Posts, follows, or moderation actions appearing on the local instance that the originating remote server has no record of sending.
Detection Strategies
- Compare the compacted JSON-LD payload against the signed portion and alert on structural differences.
- Correlate inbound federated activities with outbound confirmations from the claimed origin instance and flag activities without a matching source event.
- Hunt for anomalous spikes in Create, Announce, or Delete activities originating from a small set of remote actors.
Monitoring Recommendations
- Log every inbound ActivityPub request with full headers, signature metadata, and payload hashes for retrospective analysis.
- Monitor Misskey application logs for signature validation warnings and JSON-LD compaction errors.
- Track the version banner exposed by federated peers and alert when local or peered instances remain below 2026.5.4.
How to Mitigate CVE-2026-46713
Immediate Actions Required
- Upgrade Misskey to version 2026.5.4 or later on every operator-controlled instance.
- Audit recent inbound federated activities from before the upgrade for suspicious posts, follows, or account changes attributed to remote users.
- Rotate instance-level secrets and review moderator actions that were triggered by federated inputs during the exposure window.
Patch Information
The vulnerability is fixed in Misskey 2026.5.4. Release details are available in the Misskey 2026.5.4 GitHub release notes, and the maintainer's coordinated disclosure is documented in the GitHub Security Advisory GHSA-w8x2-gpq6-jxvf.
Workarounds
- No official workaround exists; upgrading to 2026.5.4 is the only supported remediation.
- Operators unable to upgrade immediately should restrict federation to a trusted allowlist of remote instances at the reverse proxy.
- Temporarily disable open federation and require manual approval for new remote peers until the patch is applied.
# Upgrade example for a Docker-based Misskey deployment
docker compose pull
docker compose down
docker compose up -d
docker compose exec web node --version
# Confirm the running Misskey version is 2026.5.4 or later
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
