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CVE-2026-50128

Mastodon: Spoofing of attribution domains

Medium5.3EPSS 0.18%
Published
Updated
Reserved
Assigned by
GitHub_M

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.

Scores

CVSS scores of CVE-2026-50128, by who scored it
Scored byCVSSScoreVector
GitHub_MCNA (assigner)3.1Medium5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVDNVD · Deferred3.1Medium5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS (exploitation in 30 days)
0.18% · top 92% of all CVEs (6 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: yes · Technical impact: partial
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.3.

Weakness

Affected products

  • mastodon · mastodon

    • affected >= 4.5.0-beta.1, < 4.5.11
    • affected >= 4.3.0, < 4.4.18

References (2)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .