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CVE-2026-97362 – Unauthenticated Denial of Service – Rejetto HFS2 2.0.0 through 2.4.0

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Summary

CVE-2026-97362 is an unauthenticated denial-of-service vulnerability in Rejetto HFS2 (the classic Delphi-based HTTP File Server), affecting versions 2.0.0 through 2.4.0. A single crafted HTTP request can drive the server’s request-handling logic into a non-terminating loop, hanging the sole serving thread and rendering the entire file server unresponsive to all clients until an operator manually restarts it.

Technical details

  • Root cause: the getKeyFromString() routine used by HFS2’s template/config-lookup logic ({.get ini.} macro) relies on a string-search helper that returns matches using an inclusive offset; when a match doesn’t satisfy a required "start of line" condition, the search repeats from the same position instead of advancing, producing an infinite loop.
  • Trigger condition: a multipart POST request whose filename field invokes the {.get ini.} template macro with a key argument that never matches at the start of a line (an empty key reliably reproduces this, since it is normalized to =, which always appears mid-line in name=value config entries).
  • Attack vector: network, unauthenticated, single request — no prior access or interaction with legitimate users is required.
  • Impact: complete loss of availability. HFS2 uses a single serving thread; once it enters the busy loop, the process keeps its listening port bound but stops responding to any request and consumes CPU, with no automatic recovery.

Affected software

  • Rejetto HFS2 (hfs2), versions 2.0.0 through 2.4.0, inclusive (confirmed impacted through 2.4-alpha01 – 2.4-rc07/RC8 source lines).

Severity

  • CVSS v3.1 Base Score: 7.5 (High) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  • Also rated CVSS v4.0: 8.7 (High) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: No vendor patch has been published for HFS2 at this time; HFS2 is a legacy product line largely superseded by Rejetto’s newer HFS (Node.js-based) server. Organizations should migrate off HFS2 where possible.
  • If no patch is available: restrict access to HFS2 instances to trusted internal networks only (do not expose to the internet), place the service behind a reverse proxy or WAF capable of inspecting multipart form data for {.get ini.} template patterns, and deploy process-monitoring/auto-restart to reduce downtime if the hang occurs. Review exposure of any internet-facing HFS2 deployments as a priority.

References

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