CVE-2009-4411 in acl
Summary
by MITRE
The (1) setfacl and (2) getfacl commands in XFS acl 2.2.47, when running in recursive (-R) mode, follow symbolic links even when the --physical (aka -P) or -L option is specified, which might allow local users to modify the ACL for arbitrary files or directories via a symlink attack.
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Analysis
by VulDB Data Team • 08/30/2021
The vulnerability identified as CVE-2009-4411 affects the XFS acl utilities version 2.2.47, specifically targeting the setfacl and getfacl commands when operating in recursive mode. This flaw represents a significant security weakness in Unix-like operating systems that rely on proper access control list management. The issue manifests when these commands process symbolic links during recursive operations despite the explicit use of the --physical (-P) or -L options that should prevent such behavior. The fundamental problem lies in the improper handling of symbolic links within the recursive processing logic, creating a scenario where the system fails to respect user intentions regarding link resolution.
This vulnerability operates under the principle of symlink attacks, where malicious users can manipulate the filesystem to gain unauthorized access to resources they should not be able to modify. The flaw allows local attackers to potentially modify access control lists for files and directories that they would normally not have permission to access, effectively bypassing the intended security controls. The technical implementation fails to properly distinguish between physical file system traversal and symbolic link resolution, creating a path traversal vulnerability that can be exploited through carefully crafted symlink chains. The issue is particularly dangerous because it undermines the fundamental security model of access control lists and file permissions, allowing privilege escalation through indirect means.
The operational impact of this vulnerability extends beyond simple access control bypasses, as it can enable attackers to gain persistent access to sensitive system resources or manipulate critical data structures. When combined with other exploitation techniques, this vulnerability can lead to complete system compromise, especially in environments where users have limited privileges but can manipulate symbolic links. The flaw affects systems that rely on XFS filesystems with extended attributes and access control lists, making it relevant to enterprise environments, cloud deployments, and any system where fine-grained permission control is essential. From an attack perspective, this vulnerability aligns with the MITRE ATT&CK framework under the Privilege Escalation category, specifically targeting the technique of "Exploitation for Privilege Escalation" and potentially "Path Traversal" methods.
The root cause of this vulnerability maps directly to CWE-59, which describes improper handling of symbolic links during file operations. The flaw demonstrates a failure in proper input validation and path resolution, where the system does not adequately enforce the user-specified behavior for link handling. Security practitioners should consider this vulnerability in the context of the principle of least privilege, as it allows local users to potentially escalate their privileges or gain access to restricted resources. The vulnerability also highlights the importance of proper filesystem abstraction and the need for consistent handling of symbolic links across different command-line utilities. Organizations should prioritize patching this vulnerability as it represents a fundamental flaw in access control mechanisms that could be exploited to undermine the security posture of affected systems. The fix typically involves modifying the recursive processing logic to properly respect the -P or -L flags and ensure that symbolic links are handled according to user specifications rather than following them regardless of the operational mode.