Medium severity · published Jun 24, 2026
CVE-2026-50128
Mastodon: Spoofing of attribution domains
5.3
CVSS
0.2%
EPSS
No
On KEV
Description
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.
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 8% 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, < 4.5.11; >= 4.3.0, < 4.4.18 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-50128
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-50128
github.com
https://github.com/mastodon/mastodon/security/advisories/GHSA-rwcw-vq68-g34p
github.com
https://github.com/gogs/gogs/security/advisories/GHSA-pwx3-qcgw-vh7h
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