# CVE-2026-50128: Mastodon signature verification bypass in attributionDomains spoofing

Source: https://junglewise.ai/threats/cve-2026-50128-mastodon-signature-verification-bypass-in-attributiondomains  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-24. Updated: 2026-06-24  
License: CC BY 4.0 with a link back

CVE-2026-50128 · Severity: medium · CVSS 5.3 · Published 2026-06-24

Mastodon is an open-source social networking platform. A flaw in how the software verifies author credits allows an attacker to falsely link a user's profile to unauthorized websites. This could be used to damage a user's reputation by making it appear as though they authored content on malicious or inappropriate websites.

Technologies: [Mastodon](https://junglewise.ai/threats/technologies/mastodon). Vendors: [Mastodon](https://junglewise.ai/threats/vendors/mastodon).

## 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

## References

- [https://github.com/mastodon/mastodon/security/advisories/GHSA-rwcw-vq68-g34p](https://github.com/mastodon/mastodon/security/advisories/GHSA-rwcw-vq68-g34p)

## Related threats

- [Mastodon LDAP authentication global TLS verification bypass](https://junglewise.ai/threats/cve-2026-59825-mastodon-ldap-authentication-global-tls-verification-bypass)
- [Mastodon denial of service via uncaught exception in math sanitizer](https://junglewise.ai/threats/cve-2026-50129-mastodon-denial-of-service-via-uncaught-exception-in-math)
- [Mastodon spoofing via JSON entry removal in signed activities](https://junglewise.ai/threats/cve-2026-48028-mastodon-spoofing-via-json-entry-removal-in-signed-activities)
- [Mastodon SSRF protection bypass in PrivateAddressCheck](https://junglewise.ai/threats/cve-2026-47389-mastodon-ssrf-protection-bypass-in-privateaddresscheck)
- [Mastodon signature bypass via JSON-LD restructuring](https://junglewise.ai/threats/cve-2026-46349-mastodon-signature-bypass-via-json-ld-restructuring)