Medium severity · published Jun 24, 2026
CVE-2026-46349
Mastodon: LD-Signature Bypass via JSON-LD Named-Graph Restructuring
5.3
CVSS
0.2%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 9% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
mastodon · mastodon
>= 4.5.0-beta.1, < 4.5.10 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-46349
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-46349
github.com
https://github.com/mastodon/mastodon/security/advisories/GHSA-chgx-jx3p-rf73
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