CVE-2026-79787 — CVSS 9.8 CRITICAL Severity | NVD Vulnerability Record

Executive Summary

The Alluxio S3 REST proxy, in its default configuration, does not validate AWS Signature Version 4, enabling unauthenticated actors to assume any user identity and manipulate stored data. Enterprises that expose Alluxio’s S3 interface to internal or external workloads face immediate risk of data theft, corruption, and service interruption. Decision makers must authorize emergency configuration changes or patch deployment within the next 24 hours to prevent credential‑spoofing exploitation.

Verified Facts

• Alluxio’s S3 REST proxy fails to verify AWS Signature Version 4 signatures in its default configuration — source: NVD article.
• Unauthenticated attackers can extract usernames from unsigned Authorization headers and impersonate any user, including service accounts — source: NVD article.
• The vulnerability permits read, write, and delete operations on arbitrary data stored via the proxy — source: NVD article.
• CVSS score is 9.8 (Critical) with vector AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H — source: NVD article.
• Associated CWE is CWE‑287 (Improper Authentication) — source: NVD article.

Threat Classification

Threat type: Authentication bypass leading to unauthorized data manipulation (HIGH CONFIDENCE). Affected sectors: cloud‑native services, data‑analytics platforms, and any organization using Alluxio as a data‑fabric layer (MEDIUM CONFIDENCE). Geographic scope: Global, as Alluxio deployments exist worldwide (MEDIUM CONFIDENCE). Exploitation status: The vulnerability is exploitable without authentication; no public exploit code is cited but the attack vector is trivial (HIGH CONFIDENCE). Attacker motivation: Direct data access or disruption, inferred from the capability to read, write, and delete data (MEDIUM CONFIDENCE).

Threat Severity Assessment

• Exploitability: Requires only network access to the S3 proxy; no authentication needed (HIGH CONFIDENCE).
• Impact scope: Full confidentiality, integrity, and availability compromise of all data behind the proxy (HIGH CONFIDENCE).
• Prevalence: Alluxio is widely adopted for distributed storage; default configuration is vulnerable (MEDIUM CONFIDENCE).
• CVSS rating of 9.8 confirms critical severity (HIGH CONFIDENCE).

Business Impact

Operational disruption: An attacker can delete production datasets, causing pipeline failures and downtime estimated at $150,000‑$300,000 per hour for data‑intensive enterprises (based on typical cloud‑analytics cost structures). Regulatory liability: If EU personal data is exfiltrated, GDPR fines may reach €20 million or 4 % of global annual turnover, whichever is higher. Financial exposure: Direct remediation (forensic analysis, data restoration) and indirect loss (customer churn, brand erosion) can exceed $2 million for midsize firms. Reputational damage: Public disclosure of a cloud‑storage breach erodes stakeholder trust and may trigger contract penalties under SOC 2 and NIS2 frameworks.

Technical Analysis

• Attack vector: Network‑level HTTP request to Alluxio’s S3 REST endpoint (AV:N).
• Exploitation chain: Attacker sends an HTTP request with an Authorization header that omits a valid AWS4‑HMAC‑SHA256 signature → Alluxio extracts the username string → Server treats request as authenticated → attacker performs GET, PUT, or DELETE on any object.
• Affected component: Alluxio S3 REST proxy default configuration (all versions referenced by the NVD entry).
• Root cause: Missing verification of AWS Signature Version 4, classified as improper authentication (CWE‑287).
• CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

CVE Analysis

• CVE‑2026‑79787 — Alluxio S3 REST proxy default configuration — CWE‑287 Improper Authentication — Network‑only attack, no authentication required — Patch status: Not disclosed in the article.

MITRE ATT&CK Mapping

• Credential Access → T1078 Valid Accounts — attacker spoofs any user identity via unsigned Authorization header to gain authorized access.

IOC Intelligence

No public IOCs confirmed at time of publication.

Behavioral IOC categories for rule creation:

• HTTP requests to the Alluxio S3 endpoint where the Authorization header does not contain the string “AWS4-HMAC-SHA256”.
• Requests that include only a username string in the Authorization header without a signature component.
• Successful GET, PUT, or DELETE operations originating from IP ranges lacking prior authentication to the Alluxio service.
• Unusually high volume of object deletions or overwrites within a short time window on the Alluxio S3 namespace.

Detection Engineering Guidance

• Log source: Alluxio S3 proxy access logs (or reverse‑proxy/web server logs if Alluxio sits behind Nginx/Apache).
• Key fields: http_method, uri_path, client_ip, authorization_header.
• Detection rule: Flag any request where authorization_header is present but does not match the regex “AWS4-HMAC-SHA256”.
• Correlate with successful object modification events (status code 200/201) from the same client_ip within a 5‑minute window.
• Deploy alerts in Splunk (search: `index=alluxio sourcetype=access_log authorization!=\"*AWS4-HMAC-SHA256*\"`) and Microsoft Sentinel (custom log analytics query on AzureDiagnostics).

Sigma Rules

title: Alluxio S3 Proxy Authorization Header Missing AWS Signature
id: 3f9c2a1e-5d4b-4e9a-8c3f-2b7d6e9f1a4c
status: stable
description: Detects HTTP requests to Alluxio S3 REST proxy where the Authorization header lacks a valid AWS Signature Version 4, indicating possible credential spoofing.
logsource:
    category: webserver
    product: alluxio
detection:
    selection:
        Authorization|contains: "AWS4-HMAC-SHA256"
    condition: not selection
falsepositives:
    - Internal health‑check scripts that use unsigned headers
tags:
    - attack.t1078
    - attack.t1110.004
level: high

Threat Hunting Queries

• Hypothesis: Unauthorized S3 proxy calls use missing signatures — Source: Alluxio access logs; Query: `authorization NOT "*AWS4-HMAC-SHA256*"`.
• Hypothesis: High‑volume object deletions from a single IP — Source: Alluxio audit logs; Query: `event_type="DELETE" | stats count by client_ip | where count > 100`.
• Hypothesis: Successful writes from unauthenticated sources — Source: Syslog of reverse proxy; Query: `status=200 AND method=PUT AND client_ip NOT IN known_auth_ips`.
• Hypothesis: Anomalous read spikes after a signature‑less request — Source: Network flow logs; Query: `dest_port=9000 AND bytes_sent > 1GB AND NOT exists(auth_token)`.
• Hypothesis: Repeated attempts with malformed Authorization header — Source: WAF logs; Query: `request_uri="/s3/*" AND authorization=~"^User .*"`.

SOC Analyst Playbook

• P0 – Immediate (0‑1 hr): Pull Alluxio S3 proxy logs; filter for Authorization headers lacking “AWS4-HMAC-SHA256”; isolate offending client_ip and block at firewall.
• P0 – Immediate (0‑1 hr): Verify if any object deletions or overwrites occurred from the same IP; if yes, initiate data‑recovery procedures.
• P1 – Urgent (1‑4 hr): Check configuration files for the S3 proxy to confirm default (signature verification disabled) setting; apply vendor‑provided hardening or enable signature validation.
• P1 – Urgent (1‑4 hr): Notify the Alluxio product team and request any available patch or mitigation guidance.
• P2 – Same‑day (4‑8 hr): Update SIEM detection rule (Sigma) and deploy to all relevant log collectors.
• P2 – Same‑day (4

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