CVE-2026-55103Discourse ActivityPub: Fix inbound actor validation and apply outbound request SSRF hardening
Updated under an hour ago ()
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It affects discourse-activity-pub. Add what you run to find out whether that includes you.
EPSS puts the chance of exploitation in the next 30 days at 0.20%, higher than 9% of scored CVEs.
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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.
- CVSS
- 8.6 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
- Weakness (CWE)
- CWE-345, CWE-863
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- 0.20% (percentile 9)
- Assigned by
- GitHub_M
- NVD analysis
- Deferred
- Record last updated
- Oct 15, 2026
- First seen by InfoSec Signals
- Oct 15, 2026
Affected products
discourse discourse-activity-pub discourse:activity_pub (from the name) | before 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5 | CNA record |
References
- https://github.com/discourse/discourse-activity-pub/security/advisories/GHSA-jw39-rch6-mhwfx-refsource-confirm
- https://github.com/discourse/discourse-activity-pub/commit/1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5x-refsource-misc
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.