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CVE-2026-82753 – Unauthenticated Resource Exhaustion (DoS) – ash_authentication_oauth2_server 0.3.0–

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Summary

CVE-2026-82753 is an unauthenticated resource exhaustion (denial-of-service) vulnerability in ash_authentication_oauth2_server, an Elixir/Erlang OAuth2 server extension for the Ash framework. When the optional Client ID Metadata Document (CIMD) feature is enabled, the /authorize endpoint fetches and stores metadata for any URL-shaped client_id without limits on document size, row count, or expiry, allowing attackers to exhaust database and memory resources. The issue is rated CVSS 8.2 (High) with an availability-only impact.

Technical details

  • Root cause: The resolve_client/3 function in lib/ash_authentication/oauth2_server/cimd.ex (module AshAuthentication.Oauth2Server.CIMD) fetches the CIMD document for each new URL-shaped client_id submitted to /authorize and upserts a corresponding client row, with no cap on the number of rows created and no length validation on stored fields.
  • Trigger conditions: Exploitable only when the CIMD feature is explicitly enabled (cimd_enabled?: true); CIMD is disabled by default, so unmodified default configurations are not affected.
  • Attack vector: Network-based, unauthenticated — an attacker repeatedly requests /authorize with distinct URL-shaped client IDs, causing the server to fetch attacker-controlled metadata documents.
  • Additional weakness: Fetched documents were cached before validation, so even documents that were ultimately rejected consumed cache memory for up to an hour, compounding the exhaustion effect.
  • Impact: Unbounded growth of database rows and memory/cache consumption can exhaust storage and memory resources, leading to denial of service. No confidentiality or integrity impact is claimed.
  • CWE: CWE-770 (Allocation of Resources Without Limits or Throttling).

Affected software

  • Vendor/Project: ash-project
  • Product: ash_authentication_oauth2_server (Erlang/Elixir package)
  • Affected versions: >= 0.3.0, < 0.3.1
  • Fixed version: 0.3.1 and later
  • Precondition: Only exploitable when the CIMD feature is enabled

Severity

  • CVSS v4.0 Base Score: 8.2 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade ash_authentication_oauth2_server to version 0.3.1 or later, which caps metadata fetches at 5 KiB, only caches documents after validation, and adds automatic garbage collection of client rows via a TTL mechanism on the ClientResource extension.
  • If unable to patch immediately:
    • Disable the CIMD feature if it is not required for your deployment.
    • Apply authentication requirements or rate limiting in front of the /authorize endpoint to reduce the ability of unauthenticated attackers to trigger repeated metadata fetches.
    • Monitor database growth and memory/cache usage for signs of abuse if CIMD must remain enabled prior to patching.

References

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