Riskcovery

CVE-2026-55103

Discourse ActivityPub: Fix inbound actor validation and apply outbound request SSRF hardening

State
Published
Severity
8.6 High
Published
Oct 15, 2026
Updated
Oct 28, 2026
Reserved
Jun 16, 2026

Read the record on cve.org

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.

Scores

CVSSScoreVectorSource
3.18.6 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:NGitHub_M

Weaknesses

  • CWE-345 Insufficient Verification of Data Authenticity
  • CWE-863 Incorrect Authorization

Affected Products

ProductVersions
discourse-activity-pubdiscourse
  • < 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5Affected

References

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