CVE-2026-46349

Mastodon: LD-Signature Bypass via JSON-LD Named-Graph Restructuring

State: Published
Severity: 5.3 Medium
Published: Jun 24, 2026
Updated: Jun 25, 2026
Reserved: May 13, 2026

Description

Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.5.10, 4.4.17, and 4.3.23, Mastodon's normalization of incoming activities signed with Linked-Data Signatures does not sufficiently protect the activities from a certain class of spoofing, allowing attackers to re-arrange a valid signed JSON-LD activity from a third-party actor to have it processed differently. This vulnerability is fixed in 4.5.10, 4.4.17, and 4.3.23.

Scores

CVSS	Score	Vector	Source
3.1	5.3 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N	GitHub_M

Weaknesses

CWE-347 Improper Verification of Cryptographic Signature

Affected Products

Product	Versions
mastodonmastodon	>= 4.5.0-beta.1, < 4.5.10Affected

References

https://github.com/mastodon/mastodon/security/advisories/GHSA-chgx-jx3p-rf73

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