All vulnerabilities
CVE-2026-55103GHSA-jw39-rch6-mhwf

discourse-activity-pub: Discourse ActivityPub: Fix inbound actor validation and apply outbound request SSRF hardening

discourse discourse-activity-pubApplications & CMS
Open in ThreatlineRecord JSON
CVSS
8.6High
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.20%Chance of exploitation activity in the next 30 days, higher than 9% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed inNone listedNo source names a fixed version. Check the vendor advisory below
Published15 Oct 2026Updated 15 Oct 2026CVE List

What fixes it

No source in this snapshot names a fixed version. The vendor advisories under References are the place to check.

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.

Text from CVE List

Affected versions 1

  • discourse-activity-pubaffected: < 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5CVE List

References 2