Vulnerability · Published Jun 24, 2026 · Assigned by GitHub_M

CVE-2026-46349Mastodon: LD-Signature Bypass via JSON-LD Named-Graph Restructuring

Medium 5.3

In plain English

A medium-severity security flaw in mastodon from mastodon. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities).

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.2%top 90.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected products (as reported)

Vendor	Product	Versions
mastodon	mastodon	>= 4.5.0-beta.1, < 4.5.10

Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

References

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