EUVD-2026-65699
GHSA-53ch-3jwm-f8ch
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessReach exposed Alluxio S3 REST proxy
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DeliveryCraft S3 request with unsigned Authorization header
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ExploitSet identity to target user/service account
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ExecutionProxy skips SigV4 verification
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ImpactRead, write, or delete arbitrary data
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A07:2025 - Authentication Failures
ASVS 5.0
V6 - Authentication Authentication mechanism validation
MITRE ATT&CK
2 techniques across 2 tactics: Defense Evasion, Initial Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | The Alluxio S3 REST proxy component must be deployed and network-reachable, and it must be running in its default configuration where SigV4 signature verification is not enforced - which the advisory states is the default. Given the CVSS vector (AV:N/AC:L/AT:N/PR:N/UI:N), no authentication, no user interaction, and no non-default settings are required to exploit an exposed proxy. The practical limiting factors are therefore purely deployment-based: whether the S3 REST proxy is enabled at all, and whether network access to its endpoint is restricted; installations that do not expose the S3 proxy or that front it with an external authenticating gateway are not exploitable via this path. |
| Impact | All available signals point to genuine high priority. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H) describes remote, low-complexity, unauthenticated exploitation with high confidentiality, integrity, and availability impact, and the flaw exists in the default configuration - the most dangerous combination for a network service. Mapped to an SSVC lens, exploitation is likely automatable (a simple forged HTTP header, no signature computation needed) with total technical impact over the data plane. Tempering the urgency: there is no EPSS score in the input, no KEV listing, and no public POC identified, so exploitation is not confirmed in the wild - the risk is driven by the triviality of the bug rather than observed attacks. The main real-world limiter is exposure: the S3 REST proxy must be deployed and network-reachable, which not every Alluxio installation enables. |
| Exploit ScenarioDerived | An attacker who can reach the Alluxio S3 REST proxy over the network sends a normal S3 request with a hand-crafted Authorization header naming a privileged service account, omitting or faking the SigV4 signature. Because the proxy never verifies the signature in its default configuration, it treats the request as that user and grants full read/write/delete access to their data. No credentials, user interaction, or exploit tooling is required, though no public POC is identified at time of analysis. |
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Alert meAnalysisAIv1 – Aug 25, 2026
Identity spoofing and authentication bypass in Alluxio's S3 REST proxy (versions through 2.9.5) lets remote unauthenticated attackers impersonate any user because the proxy does not verify AWS Signature Version 4 signatures in its default configuration. By reading the username directly from an unsigned Authorization header, an attacker can assume the identity of arbitrary users and service accounts to read, write, and delete data. Reported by VulnCheck with a CVSS 4.0 base score of 9.3; no public exploit identified at time of analysis, and it is not listed in CISA KEV.
RemediationAI
No vendor-released patch version is identified in the available data (the advisory describes Alluxio 'through 2.9.5' as affected and the referenced GitHub issue #18755 tracks the report, but no fixed release is confirmed here), so treat fixed-version claims cautiously and confirm with Alluxio before relying on an upgrade. As concrete compensating controls: restrict network access to the S3 REST proxy endpoint so it is only reachable from trusted client hosts (firewall/allowlist the proxy port), or disable the S3 REST proxy entirely if it is not required - the trade-off is that S3-protocol clients will lose access to Alluxio data. Place the proxy behind an authenticating reverse proxy or gateway that enforces its own credential check before requests reach Alluxio, and monitor proxy access logs for requests bearing unsigned or malformed Authorization headers or unexpected user/service-account identities. Track https://github.com/Alluxio/alluxio/issues/18755 and the VulnCheck advisory for an official fixed version and apply it once published.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in euvd
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Alluxio is an open-source data orchestration / virtual distributed file system layer that sits between compute frameworks (Spark, Presto, ML pipelines) and underlying storage. It exposes an S3-compatible REST proxy so S3 clients can access Alluxio-managed data. AWS SigV4 is a keyed-HMAC request-signing scheme where the client proves possession of a secret key by signing the canonical request; the server is supposed to recompute and compare that signature. This flaw is CWE-287 (Improper Authentication): the proxy's S3RestUtils logic (core/server/proxy/src/main/java/alluxio/proxy/s3/S3RestUtils.java in v2.9.5) parses the identity/access-key portion of the Authorization header but never validates the accompanying signature, so any value presented as the requesting user is trusted. The affected component is identified by CPE cpe:2.3:a:alluxio:alluxio and, per the VulnCheck advisory, spans Alluxio through 2.9.5.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
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
Remote, low-complexity, unauthenticated bypass in default config with full read/write/delete over data yields PR:N, AC:L, and high C/I/A; scope unchanged as impact stays within the proxy's data plane.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
DescriptionCVE.org
Alluxio's S3 REST proxy fails to verify AWS Signature Version 4 signatures in its default configuration, allowing unauthenticated attackers to spoof user identity. Attackers can extract usernames from unsigned Authorization headers and impersonate any user, including service accounts, to read, write, and delete arbitrary data.
Executive ViewAI
Alluxio's S3 REST proxy (versions through 2.9.5) contains a critical authentication bypass vulnerability that allows remote attackers to impersonate any user and gain full access to data. Organizations relying on Alluxio for data management face immediate risk of unauthorized data access, modification, and deletion without requiring credentials. Urgent mitigation is required to prevent data breach and maintain system integrity.
No vendor-released patch identified at time of analysis. Interim mitigations include: (1) network segmentation restricting proxy access to trusted internal IP ranges only; (2) deployment of WAF or API gateway layer to externally validate AWS Signature Version 4 signatures before requests reach Alluxio; (3) disable S3 REST proxy entirely if not operationally essential; (4) comprehensive access and audit logging with real-time alerting for signature validation failures; (5) enforce mutual TLS (mTLS) authentication at the network boundary if possible.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
An issue in Alluxio v.2.9.3 and before allows an attacker to execute arbitrary code via a crafted script to the username
In Alluxio before 2.7.3, the logserver does not validate the input stream. Rated critical severity (CVSS 9.8), this vuln
Exploit-DB