Vulnerability details
CVE-2026-55103
discourse discourse-activity-pub
Discourse ActivityPub: Fix inbound actor validation and apply outbound request SSRF hardening
CVSS 3.1
8.6High
Official 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.
CVSS scores
| Score | Version | Source | Vector |
|---|---|---|---|
| 8.6High | 3.1 | CVEProject cvelistV5 (CNA) (GitHub_M) | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N |
Affected products
| Vendor | Product | Versions | Source |
|---|---|---|---|
| discourse | discourse-activity-pub | < 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5 | CVEProject cvelistV5 (CNA) |
References and advisories
2
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Details
- Published
- 2026-10-15
- Last updated
- 2026-10-28
- State
- Published
- Assigner (CNA)
- GitHub_M
Exploit prediction (EPSS)
0.2%
Probability of exploitation in 30 days
9.8%
Percentile (among all CVEs)
SSVC assessment (CISA)
- Automatable
- Yes
- Exploitation
- None
- Technical impact
- Partial
Weaknesses (CWE)
- CWE-345Insufficient Verification of Data Authenticity
- CWE-863Incorrect Authorization