CVE-2026-49991 in RustFS
Summary
by MITRE • 06/26/2026
RustFS is a distributed object storage system built in Rust. In 1.0.0-beta.4, authenticated users with only PutObject permission on their own bucket can exploit a path traversal vulnerability in the Snowball auto-extract feature to write arbitrary objects into other users' buckets, completely breaking multi-tenant isolation. The vulnerability chains three flaws: No ../ sanitization in tar entry key normalization; IAM wildcard matching uses raw (uncleaned) paths; and Filesystem path cleaning resolves ../ across bucket boundaries.
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Analysis
by VulDB Data Team • 06/26/2026
The RustFS distributed object storage system contains a critical path traversal vulnerability in version 1.0.0-beta.4 that fundamentally undermines multi-tenant security isolation. This vulnerability affects authenticated users who possess only PutObject permissions on their own buckets, yet allows them to escalate their privileges and write objects into other users' buckets through the Snowball auto-extract feature. The flaw represents a sophisticated chain of three interconnected technical weaknesses that together create an exploitable condition for unauthorized data access and modification across tenant boundaries.
The primary technical flaw exists in the tar entry key normalization process where the system fails to sanitize path traversal sequences such as ../ within archive entries. This absence of proper input validation allows maliciously crafted tar files to contain entries with relative path components that can escape the intended bucket boundaries during extraction. The second vulnerability lies in the IAM permission system's wildcard matching implementation which operates on raw, uncleaned paths rather than normalized ones. When users attempt to access resources using wildcard patterns, the system matches against the original path strings without first removing traversal sequences, creating an opportunity for exploitation.
The third component of this vulnerability chain involves filesystem path cleaning operations that incorrectly resolve ../ sequences even when they cross bucket boundaries. This design flaw allows path normalization to traverse upward in the directory structure beyond the confines of individual user buckets, effectively bypassing the intended access controls. The combination of these three vulnerabilities creates a complete path traversal exploit where an authenticated user can manipulate tar archive entries to write files into arbitrary locations within other users' storage spaces.
This vulnerability directly maps to CWE-22 Path Traversal and CWE-352 Cross-Site Request Forgery, while also exhibiting characteristics consistent with ATT&CK technique T1078 Valid Accounts and T1566 Phishing. The operational impact is severe as it completely breaks the fundamental multi-tenant isolation that distributed storage systems rely upon for security. An attacker can use this vulnerability to access sensitive data belonging to other users, inject malicious content into shared buckets, or potentially escalate privileges further within the system. Organizations using RustFS in production environments face significant risk of data leakage and unauthorized access when this vulnerability remains unpatched.
The recommended mitigations include implementing comprehensive path sanitization at multiple layers of the system architecture, particularly around tar entry processing and IAM permission evaluation. All path traversal sequences must be normalized and validated before any filesystem operations occur, with strict boundaries enforced between user buckets. The IAM system should clean paths before performing wildcard matching to prevent exploitation of raw path inputs. Additionally, implementing proper access control checks during file system operations can prevent ../ resolution across bucket boundaries. Regular security audits should validate that all input paths are properly sanitized and that the system maintains strict isolation between tenant storage spaces.