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CVE-2026-73937 – Denial of Service / Unauthorized Data Access – Oracle Helidon 4.5.0 (Imperative Web

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Summary

CVE-2026-73937 is a high-severity vulnerability (CVSS 3.1: 8.2) affecting the Imperative Web Server component of Oracle Helidon. An unauthenticated attacker with network access via HTTP/2 can trigger the flaw to cause the server to hang or crash (denial of service) and to gain unauthorized read access to certain Helidon-accessible data. The issue is rated "easily exploitable" by Oracle, requiring no credentials and no user interaction, making it a significant risk for internet-facing Helidon deployments.

Technical details

  • Root cause: A flaw in Oracle Helidon’s Imperative Web Server when handling HTTP/2 connections/requests.
  • Trigger conditions: An attacker sends crafted HTTP/2 traffic to a network-reachable Helidon Imperative Web Server instance; no authentication or user interaction is required.
  • Attack vector: Network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N).
  • Impact: High availability impact — the server can hang or crash repeatedly, resulting in denial of service — combined with low confidentiality impact, allowing unauthorized read access to some accessible data. Integrity is not affected (I:N), and scope is unchanged (S:U).

Affected software

  • Oracle Helidon, version 4.5.0 (Imperative Web Server component), as identified in the CVE record.
  • Oracle’s August 2026 Critical Security Patch Update advisory lists the broader set of Helidon versions evaluated as part of this update cycle: 1.4.19, 1.4.20, 3.2.18, 3.2.19, 3.2.20, 4.5.0, 4.5.1, and 4.5.3. Organizations running any Helidon 1.4.x, 3.2.x, or 4.5.x release should confirm their exact version against Oracle’s advisory to determine applicability.

Severity

  • CVSS v3.1 Base Score: 8.2 (HIGH)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Mitigation and recommended actions

  • Immediate: Apply the fixes provided in Oracle’s August 2026 Critical Security Patch Update (CSPU) advisory and upgrade Oracle Helidon to the latest patched release in your track (e.g., the 4.5.x line beyond 4.5.0, per Oracle’s advisory). Confirm the exact remediated version for your deployed branch (1.4.x, 3.2.x, or 4.5.x) directly against Oracle’s advisory before upgrading.
  • If immediate patching is not possible:
    • Restrict network exposure of Helidon Imperative Web Server endpoints to trusted networks only; avoid direct internet exposure where feasible.
    • Where supported, disable or restrict HTTP/2 on affected services until patched, monitoring for compatibility impacts.
    • Monitor for abnormal server hangs, crashes, or repeated restarts that could indicate exploitation attempts, and review logs for anomalous HTTP/2 traffic patterns.
    • Apply network-layer controls (firewalls, WAFs, or reverse proxies) that can filter malformed or abusive HTTP/2 traffic as a compensating control.

References

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