CVE-2026-55103
Last modified
CVE-2026-55103 is a high-severity vulnerability rated 8.6/10 on the CVSS scale. 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. EPSS estimates a 0.20% chance of exploitation in the next 30 days.
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.
Metrics
Weakness Enumeration
Affected Software
Source: CNA advisory (CVE.org). NVD analysis pending.
| Vendor | Product | Versions |
|---|---|---|
| discourse | discourse-activity-pub | < 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5 |
References
Timeline
- Published
- Last Modified
- Status
- Deferred
Frequently Asked Questions
What is CVE-2026-55103?
How severe is CVE-2026-55103?
How do I fix CVE-2026-55103?
How Strix Helps
- Uncovering a hidden BOLA in Appsmith's snapshot logicStrix autonomously discovered a BOLA/IDOR vulnerability in Appsmith's snapshot deletion path.
- Same Subject, Wrong User: A Cross-Issuer Account Takeover in n8nStrix found an identity-binding bug in n8n's token-exchange flow enabling account takeover.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
Related CVEs from 2026
- CVE-2026-55096fast-mcp-telegram is a Telegram MCP Server. Prior to version…7.1
- CVE-2026-55098Arc is an open, SQL-native time-series database for telemetr…6.5
- CVE-2026-55099icalendar is an RFC 5545 compatible parser and generator of …7.5
- CVE-2026-5510The GiveWP – Donation Plugin and Fundraising Platform plugin…6.4
- CVE-2026-55100hashi-vault-js is a Node.js module for interacting with the …8.7
- CVE-2026-55102hashi-vault-js is a Node.js module for interacting with the …5.8
- CVE-2026-55105Joplin is an open source note-taking and to-do application t…7.7
- CVE-2026-55106authentik is an open-source identity provider. Prior to 2026…5.3
- CVE-2026-55107Kobako is a Ruby gem that embeds a Wasm-isolated mruby inter…10
- CVE-2026-55108KubeVela is an open source application delivery platform. Pr…8.5
- CVE-2026-5511In the web management interface of Archer AX72 (SG) v1, the …2.7
- CVE-2026-55110A malicious actor who lures an authenticated user to a malic…6.1
Are you affected by CVE-2026-55103?
Run a free Strix scan to check your systems for this vulnerability.
Scan your code nowSource: NVD / NIST