CVE-2026-79787 in Alluxio
Summary
by MITRE • 08/25/2026
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.
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Analysis
by VulDB Data Team • 08/25/2026
The vulnerability identified in Alluxio's S3 REST proxy represents a critical authentication bypass that fundamentally undermines the integrity of access controls within distributed storage systems. In its default configuration, the component responsible for translating standard Amazon S3 API requests into operations on underlying file systems fails to properly validate AWS Signature Version 4 signatures. This cryptographic verification process is essential for ensuring that incoming requests are genuinely authorized by the claimed identity and have not been tampered with during transit. By neglecting this step, Alluxio exposes a severe flaw where the system accepts requests without confirming their authenticity, effectively treating unauthenticated traffic as legitimate user activity.
The technical mechanism of this exploitation relies on the structure of HTTP Authorization headers used in AWS Signature Version 4 protocols. These headers contain metadata about the request, including the identity of the requester and cryptographic signatures proving that identity. An attacker can craft malicious requests where they either omit the signature entirely or provide a malformed one while retaining other parts of the header. The vulnerable implementation parses these headers to extract the username field but skips the subsequent verification of the digital signature against AWS secret keys. This allows an unauthenticated actor to spoof any user identity, including high-privilege service accounts that typically possess broad permissions within the cluster environment.
The operational impact of this vulnerability is severe and multifaceted, primarily centering on unauthorized data access and manipulation. Since attackers can impersonate arbitrary users, they gain the ability to read sensitive files stored in Alluxio caches or underlying storage layers such as HDFS, S3, or local disks. Beyond mere eavesdropping, the flaw permits write operations, allowing adversaries to inject malicious code, corrupt datasets, or overwrite critical configuration files. Furthermore, the capability to delete arbitrary data poses a significant risk of denial of service and permanent information loss. The ability to impersonate service accounts is particularly dangerous because these identities often operate with elevated privileges that regular user accounts do not possess, potentially leading to broader compromise of the entire distributed infrastructure.
This flaw aligns directly with CWE-287, which describes Improper Authentication, as well as CWE-306, Missing Authentication for Critical Function, since the core function of validating request origin is absent. From a threat modeling perspective consistent with MITRE ATT&CK frameworks, this vulnerability facilitates Identity Impersonation and can be leveraged to achieve Initial Access or Lateral Movement within a cloud-native architecture. Attackers may use techniques such as Request Smuggling or Header Injection to exploit the parsing logic that extracts usernames without verifying signatures. The lack of signature verification also violates principles outlined in OWASP API Security Top 10, specifically relating to Broken Object Level Authorization and insufficient input validation for security-critical parameters.
Mitigation strategies must prioritize immediate remediation through configuration changes and software updates. Administrators should immediately update Alluxio to a patched version where the S3 REST proxy enforces strict signature verification by default. If an upgrade is not feasible, temporary mitigations include disabling the S3 REST proxy endpoint if it is not strictly required for business operations or restricting network access to this service via firewall rules and security groups to trusted IP ranges only. Additionally, implementing Web Application Firewalls with specific rule sets capable of detecting malformed AWS signatures can provide a layer of defense in depth. Long-term architectural improvements should involve adopting mutual TLS authentication and ensuring that all API gateways enforce strict cryptographic validation before processing any user identity claims.