Vulnerability · Published Jun 24, 2026 · Assigned by GitHub_M

CVE-2026-50128Mastodon: Spoofing of attribution domains

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 8% of all known vulnerabilities).

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.2%top 92.1% 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. 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 products (as reported)

Vendor	Product	Versions
mastodon	mastodon	>= 4.5.0-beta.1, < 4.5.11>= 4.3.0, < 4.4.18

Weakness: CWE-354 · 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-rwcw-vq68-g34p x_refsource_CONFIRM
https://github.com/gogs/gogs/security/advisories/GHSA-pwx3-qcgw-vh7h exploit