CVE Catalog

CVE-2026-55103

HighCVSS 8.6
Published: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.20%

9th percentile - higher than 9% of all known CVEs

Summary

Discourse ActivityPub prior to commit 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5 does not sufficiently verify that the actor authenticated by the signed request matches the Activity actor and owns the referenced federated post. These missing identity and ownership checks allow a remote attacker to edit, delete, or reply to federated posts without the required permissions.

Risk Assessment

An attacker can modify or delete federated content and post replies without authorization, compromising data integrity and trust in the ActivityPub federation.

Recommendation

Update Discourse ActivityPub to commit 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5 or later.

Related vulnerabilities

Original NVD description (English source)

Discourse ActivityPub adds ActivityPub support to Discourse. Prior to commit 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5, inbound ActivityPub processing does not sufficiently verify that the actor authenticated by the signed request matches the Activity actor and owns the referenced federated post. A remote attacker can exploit these missing identity and ownership checks to edit, delete, or reply to federated posts without the required permissions. This vulnerability is fixed with commit 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS