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CVE-2026-58178 – Denial of Service (Uncontrolled Recursion in ESI Plugin) – Apache Traffic Server 8.

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Summary

CVE-2026-58178 is an uncontrolled recursion vulnerability (CWE-674) in the Edge Side Includes (ESI) plugin of Apache Traffic Server. A remote, unauthenticated attacker can leverage the plugin to recursively fetch attacker-controlled URLs without bounds, exhausting server resources and resulting in a denial-of-service condition. The issue carries a CVSS v3.1 base score of 7.5 (HIGH).

Technical details

  • Root cause: The ESI plugin fails to enforce bounds on recursion when processing Edge Side Includes directives, allowing nested/recursive fetches to grow without limit (CWE-674: Uncontrolled Recursion).
  • Trigger conditions: Requires that the ESI plugin is enabled and that ESI processing can be induced to fetch attacker-controlled URLs, which are then recursively resolved.
  • Attack vector: Network (AV:N). The vulnerability is remotely reachable and requires no authentication or user interaction.
  • Impact: High availability impact. Uncontrolled recursion exhausts server resources, causing a denial of service for the affected Traffic Server instance. There is no confirmed impact to confidentiality or integrity.

Affected software

  • Apache Traffic Server 8.0.0 through 8.1.9
  • Apache Traffic Server 9.0.0 through 9.2.14
  • Apache Traffic Server 10.0.0 through 10.1.3

Severity

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

Mitigation and recommended actions

  • Immediate: Upgrade to Apache Traffic Server 9.2.15 or 10.1.4 (or later), which contain the fix. Note that no fixed release is listed for the 8.x branch; users running 8.0.0–8.1.9 should migrate to a supported, patched release line.
  • If no patch can be applied immediately: Disable the ESI plugin if it is not required, or restrict/validate the URLs the ESI plugin is permitted to fetch so attacker-controlled recursive fetches cannot be triggered. Apply upstream network controls to limit exposure of the affected service until patching is complete.

References

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