CVE-2026-50128
CVE-2026-50128 is a medium-severity vulnerability with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-354.
Key facts
- Severity: Medium (CVSS 3.x base score 5.3)
- EPSS exploit prediction: 0% (3rd percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-39059
- Weakness: CWE-354
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-50128?
- 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.
- How severe is CVE-2026-50128?
- CVE-2026-50128 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
- Is CVE-2026-50128 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (3rd percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2026-50128?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-50128 have an EU (EUVD) identifier?
- Yes. CVE-2026-50128 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39059.
- When was CVE-2026-50128 published?
- CVE-2026-50128 was published on 2026-06-24 and last updated on 2026-06-25.
References
- https://github.com/mastodon/mastodon/security/advisories/GHSA-rwcw-vq68-g34p
- https://github.com/gogs/gogs/security/advisories/GHSA-pwx3-qcgw-vh7h
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