CVE-2026-55103

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.

CVSS v3 8.6 HIGH

8.6^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 4.0

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact NONE

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://github.com/discourse/discourse-activity-pub/commit/1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5
https://github.com/discourse/discourse-activity-pub/security/advisories/GHSA-jw39-rch6-mhwf

Configurations

No configuration.

History

15 Oct 2026, 18:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-15 18:17

Updated : 2026-10-28 21:16

NVD link : CVE-2026-55103

Mitre link : CVE-2026-55103

CVE.ORG link : CVE-2026-55103

JSON object : View

Products Affected

No product.

CWE

CWE-345

Insufficient Verification of Data Authenticity

CWE-863

Incorrect Authorization

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