Quick answers
- Is CVE-2026-50128 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-50128 being exploited in the wild.
- How severe is CVE-2026-50128?
- Medium severity, with a CVSS score of 5.3, published 24 June 2026.
- Which products and versions are affected?
- Mastodon >= 4.3.0, < 4.4.18; >= 4.5.0, < 4.5.11.
- Is there a fix for CVE-2026-50128?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-50128 attacked?
- It is attacked over the network, in a hosted service.
- Am I affected by CVE-2026-50128?
- Check whether you run Mastodon at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A vulnerability exists in Mastodon's implementation of the 'attributionDomains' JSON-LD term. Due to a definition error, Linked Data Signatures on the 'toot:attributionDomains' property are ineffective. A remote, unauthenticated attacker can intercept and modify a legitimately signed 'Update' activity to change the attribution domains. Because the signature verification is bypassed for this specific property, remote Mastodon servers will accept the modified data, allowing for false attribution of web content to a specific user profile. The issue is resolved in versions 4.4.18 and 4.5.11.
Affected products
- Mastodon Mastodon >= 4.3.0, < 4.4.18; >= 4.5.0, < 4.5.11
Timeline
- 2026-06-03: advisory: GitHub Security Advisory published
- 2026-06-24: disclosed: NVD publication date