CVE-2026-50128

Summary

Mastodon is a free, open-source social network server based on ActivityPub. From 4.3.0 until 4.5.11 and 4.4.18, Mastodon has a feature to let websites credit authors of their articles. To prevent false attribution claims, Mastodon uses the attributionDomains JSON-LD term, however, an error in how it is defined makes Linked Data Signatures on the toot:attributionDomains property ineffective. An attacker can arbitrarily modify the attributionDomains value of a legitimately signed Update activity and bypass Mastodon’s signature verification. This vulnerability is fixed in 4.5.11 and 4.4.18.

Affected Software

VendorProductVersion RangeStatus
mastodonmastodon>= 4.5.0-beta.1, < 4.5.11affected
mastodonmastodon>= 4.3.0, < 4.4.18affected

Weaknesses

  • CWE-354: CWE-354: Improper Validation of Integrity Check Value

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: yes
    • Technical Impact: partial

Additional References

References