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

Type: advisorySource: Official CVE List1 source record

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.

Announced Source revision 1
Original source ↗

CVE-2026-55103

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-55103

discourse-activity-pub

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "vendor": "discourse",
    "product": "discourse-activity-pub",
    "versions": [
      {
        "status": "affected",
        "version": "< 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5"
      }
    ]
  }
]
Related CVEs
CVE-2026-55103

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#29875 · Revision 1
Added to Heist Feed
Publisher date
Read the original announcement