Linked Data Signature Bypass in Mastodon Social Network Server
CVE-2026-50128

5.3MEDIUM

Key Information:

Vendor

Mastodon

Status
Mastodon
Vendor
CVE Published:
24 June 2026

What is CVE-2026-50128?

Mastodon is an open-source social network server built on the ActivityPub protocol. A vulnerability in versions 4.3.0 to 4.5.11 and 4.4.18 relates to the attributionDomains JSON-LD term. Due to improper definition, the verification of Linked Data Signatures on the toot:attributionDomains property becomes ineffective, allowing attackers to manipulate the attributionDomains value in legitimately signed Update activities. This flaw could lead to false attribution claims, making it crucial for users to upgrade to versions 4.5.11 or 4.4.18, where this issue is resolved.

Affected Version(s)

mastodon >= 4.5.0-beta.1, < 4.5.11 < 4.5.0-beta.1, 4.5.11

mastodon >= 4.3.0, < 4.4.18 < 4.3.0, 4.4.18

References

https://github.com/mastodon/mastodon/security/advisories/...
x_refsource_CONFIRM

CVSS V3.1

Score:
5.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.