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CVE-2026-88592 – Server-Side Request Forgery (SSRF) – kkFileView ≥ 4.2.0

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Summary

CVE-2026-88592 is a critical Server-Side Request Forgery (SSRF) vulnerability affecting kkFileView, an open-source online document preview and file conversion platform. The flaw resides in the /getCorsFile endpoint, where a mismatch between the parameter validated by the access-control filter and the parameter actually fetched by the controller allows an unauthenticated attacker to force the server to make arbitrary outbound requests and retrieve the response content. The issue carries a CVSS v3.1 base score of 9.1 (Critical) and affects kkFileView 4.2.0 and later.

Technical details

  • Root cause: The TrustHostFilter validates the first non-empty parameter it encounters, in a fixed priority order (url → currentUrl → urlPath → urls), against a configured trusted-host whitelist. However, the OnlinePreviewController handling the /getCorsFile endpoint only reads and fetches the urlPath parameter, regardless of which parameter passed validation.
  • Trigger conditions: An attacker sends a single request to /getCorsFile supplying two parameters simultaneously: url set to a whitelisted/decoy address (which satisfies the filter’s check) and urlPath set to the actual target the attacker wants the server to fetch (e.g., an internal/intranet address). Because the filter only inspects url and stops there, the malicious urlPath value is never validated.
  • Attack vector: Network-based, no authentication or user interaction required (AV:N/AC:L/PR:N/UI:N).
  • Impact: The server fetches attacker-specified URLs — including internal-only or loopback addresses — and echoes the response body back to the attacker, enabling reconnaissance and data exfiltration against internal services, cloud metadata endpoints, and other network-restricted resources reachable from the kkFileView host. The scoring reflects high confidentiality and integrity impact with no availability impact.

Affected software

  • kkFileView versions 4.2.0 and later (the vulnerable parameter-validation logic has been confirmed to persist through current master builds)

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: No official patched release has been published by the kkFileView project as of this writing. Security teams should monitor the project’s release channel for a fix that enforces consistent validation between the filter and the controller (i.e., validating the same parameter that is actually fetched).
  • Workarounds (until a patch is available):
    • Disable the affected endpoint entirely by setting kk.Getcorsfile = false in the kkFileView configuration if cross-origin file fetching is not required.
    • Deploy a WAF/reverse-proxy rule to strip or block the url and currentUrl parameters on requests to /getCorsFile, forcing all validation to occur against the actual fetched parameter.
    • Restrict network egress from the kkFileView host so it cannot reach internal-only services, loopback addresses, or cloud metadata endpoints, limiting the impact of any SSRF even if exploited.
    • Restrict inbound access to the kkFileView service to trusted networks only, reducing exposure to unauthenticated internet-based exploitation.

References

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