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CVE-2026-79787 – Authentication Bypass / Full Data Compromise – Alluxio S3 REST Proxy (through 2.9.5

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Summary

CVE-2026-79787 is an authentication bypass (CWE-287) in Alluxio’s S3 REST proxy, affecting all Alluxio versions through 2.9.5. The proxy fails to cryptographically verify AWS Signature Version 4 signatures in its default configuration, allowing an unauthenticated network attacker to spoof the identity of any user, including service accounts. This is rated CRITICAL, with a CVSS v4.0 base score of 9.3.

Technical details

  • Root cause: the proxy code that parses S3 API requests extracts the username directly from the Credential field of the AWS4-HMAC-SHA256 Authorization header, but never validates the accompanying signature.
  • Trigger condition: exploitable whenever the alluxio.s3.rest.authentication.enabled property is left at its default value of false, which skips signature verification entirely.
  • Attack vector: network, no authentication or user interaction required; an attacker only needs network access to the Alluxio proxy service (default port 39999) and can supply an arbitrary username in a syntactically valid but unsigned Authorization header.
  • Impact: full impersonation of any Alluxio user, including service accounts, enabling unauthorized read, write, and delete operations on data accessible to the impersonated identity, up to namespace-wide access if a superuser account is spoofed.

Affected software

  • Alluxio (Alluxio/alluxio), all versions from 0 through 2.9.5, when the S3 REST proxy is enabled with default settings.

Severity

  • CVSS v4.0: 9.3 (CRITICAL) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
  • CVSS v3.1: 9.8 (CRITICAL) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: no fixed release has been published by the Alluxio project as of this writing; monitor the Alluxio project and vendor channels for a patched release and upgrade as soon as one is available.
  • Workarounds: explicitly set alluxio.s3.rest.authentication.enabled=true to enforce signature validation on the S3 REST proxy; restrict network access to the proxy port (default 39999) to trusted hosts only, e.g. via firewall rules or network segmentation; avoid exposing the S3 REST proxy directly to untrusted networks or the public internet; review proxy access logs for requests using unexpected or unsigned Authorization headers.

References

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