# CVE-2026-50128

## Summary

- **CVE ID:** CVE-2026-50128
- **Severity:** MEDIUM
- **CVSS Score:** 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **CWE:** CWE-354
- **Published:** Jun 24, 2026
- **Last Modified:** Jun 25, 2026

## 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

- mastodon — mastodon (>= 4.5.0-beta.1, < 4.5.11)
- mastodon — mastodon (>= 4.3.0, < 4.4.18)

## References

- [CNA](https://github.com/mastodon/mastodon/security/advisories/GHSA-rwcw-vq68-g34p)
- [CISA-ADP](https://github.com/gogs/gogs/security/advisories/GHSA-pwx3-qcgw-vh7h)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.18%
- **EPSS Percentile:** 7.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._