CVE-2026-48028

Mastodon: Removal of integrity-protected JSON entries from signed activities

State: Published
Severity: 6.5 Medium
Published: Jun 24, 2026
Updated: Jun 25, 2026
Reserved: May 20, 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 threat actors to remove JSON entries from valid signed activities from a third-party actor. This vulnerability is fixed in 4.5.10, 4.4.17, and 4.3.23.

Scores

CVSS	Score	Vector	Source
3.1	6.5 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L	GitHub_M

Weaknesses

CWE-354 Improper Validation of Integrity Check Value

Affected Products

Product	Versions
mastodonmastodon	>= 4.5.0-beta.1, < 4.5.10Affected >= 4.4.0-beta.1, < 4.4.17Affected < 4.3.23Affected

References

https://github.com/mastodon/mastodon/security/advisories/GHSA-53m7-2wrh-q839

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