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CVE-2026-55103 Details

ANALYZED

This CVE record has been analyzed and enriched by NVDAPI.com as an independent party.

Description

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.

Metrics

CVSS 3.x Severity and Vector Strings:

VolerionCVSS-B:4.3 MEDIUMVector:CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

CNA: [email protected]CVSS-B:8.6 HIGHVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/discourse/discourse-activity-pub/commit/1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5	[email protected]	Source CodeVendor
https://github.com/discourse/discourse-activity-pub/security/advisories/GHSA-jw39-rch6-mhwf	[email protected]	AdvisoryRemedyVendor

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-345	Insufficient Verification of Data Authenticity	[email protected]
CWE-863	Incorrect Authorization	[email protected]

Affected Products

Product	Versions
Discourse ActivityPub	<= 3d5d6e7
CPE No CPEs found in CPE dictionary for this product. Remediation Upgrade: 3d5d6e7moderate effort

Change History

2 change records found show changes

Date	Action	Recorded By
Oct 28, 2026	CVE Modified	CISA-ADP
Oct 15, 2026	New CVE Received	[email protected]