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CVE-2026-63101 – Authentication Bypass / Unauthenticated Member Roster Disclosure – Open Event Se…

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Summary

CVE-2026-63101 is a high-severity missing authentication vulnerability (CWE-306) affecting Open Event Server (fossasia/open-event-server) through version 1.19.1. The flaw allows unauthenticated remote attackers to export the complete member roster — including email addresses, names, join dates, and roles — for any group hosted on the platform, with no credentials required at any step. The vulnerability carries a CVSS v4.0 score of 8.7 (HIGH) and a CVSS v3.1 score of 7.5 (HIGH).

Technical details

  • Root cause: Two API endpoints in the Open Event Server codebase are missing authentication decorators entirely. The export trigger endpoint (POST /v1/group/<group_id>/export/followers/csv, located in app/api/exports.py) and the task status polling endpoint (GET /v1/tasks/<task_id>, located in app/api/celery_tasks.py) both lack any @jwt_required, @is_admin, or equivalent access control decorator, while comparable endpoints in the same codebase correctly enforce authentication.
  • Trigger conditions: No authentication or special conditions are required. Any network-reachable instance is exploitable. Group IDs are sequential integers and can be enumerated via brute-force starting from 1.
  • Attack vector: Fully remote, unauthenticated, three-step chain: (1) send an unauthenticated POST request to the group followers CSV export endpoint using an enumerated group ID; (2) extract the task identifier from the response; (3) poll the unauthenticated task status endpoint until the task completes and a download URL is returned.
  • Impact: Bulk exfiltration of personally identifiable information (PII) for all group members across the platform — including full names, email addresses, group join dates, and role assignments (Owner, Organizer, Follower). This data can be leveraged for targeted phishing campaigns, spam, or further account compromise.

Affected software

  • Open Event Server (fossasia/open-event-server) — all versions through 1.19.1

Severity

  • CVSS v3.1 Base Score: 7.5 (HIGH)
  • Vector string: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Mitigation and recommended actions

  • No patch is available. The fossasia/open-event-server repository was archived on May 21, 2026 and is no longer actively maintained. No fix has been released.
  • Immediate action — decommission or isolate: Organizations running exposed Open Event Server instances should take them offline or restrict all inbound network access at the perimeter (firewall/WAF) as a matter of urgency, as no vendor-supported remediation path exists.
  • Network-level workaround: Until decommissioning is possible, block or rate-limit access to the /v1/group/*/export/followers/csv and /v1/tasks/* API endpoints via a WAF or reverse proxy to reduce exposure.
  • Audit exposed instances: Review internet-facing deployments for evidence of unauthorized access to the affected export and task endpoints in server logs.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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