CVE-2026-50128 Mastodon: Spoofing of attribution domains
Attackers can bypass signature verification to spoof author attribution domains in Mastodon social network posts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-50128?
CVE-2026-50128 is a medium-severity vulnerability in mastodon, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-354
Which versions are affected by CVE-2026-50128?
1 open source package ship an affected version, including mastodon.
| Package | Affected | Fixed in |
|---|---|---|
mastodon Bitnami | From 4.3.0 | 4.4.18, 4.5.11 |
How do I fix CVE-2026-50128?
Upgrade mastodon to a fixed version for your release line: 4.4.18 or 4.5.11.
Is CVE-2026-50128 being exploited?
There is no known exploitation of CVE-2026-50128 in the wild and no public exploit code.
Sources
Also known as BIT-mastodon-2026-50128.