---
id: CVE-2026-55103
title: Discourse ActivityPub adds ActivityPub support to Discourse
summary: >-
  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…
severity: high
cvss: 8.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N'
cwe:
  - CWE-345
  - CWE-863
vendor: discourse
product: discourse-activity-pub
affected:
  - discourse-activity-pub < 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5
published: '2026-10-15'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T18:17:27.163'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55103'
references:
  - url: >-
      https://github.com/discourse/discourse-activity-pub/commit/1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5
    label: security-advisories@github.com
  - url: >-
      https://github.com/discourse/discourse-activity-pub/security/advisories/GHSA-jw39-rch6-mhwf
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-15T18:23:58.449Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.