ACL Symlink Traversal Leading to Privilege Escalation

Executive Summary

The vulnerability in acl versions before 2.4.0 is a symlink traversal flaw in the libacl pathname-based functions acl_get_file(), acl_set_file(), acl_extended_file(), and acl_delete_def_file().

It allows local attackers to escalate privileges by replacing any component of a pathname with a symbolic link. This means that if an attacker controls any part of a pathname processed by a privileged program, they can redirect access control list (ACL) read or write operations to arbitrary files or directories.

As a result, attackers can manipulate ACLs without authorization and escalate their local privileges.

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Compliance Impact

This vulnerability allows local attackers to escalate privileges by manipulating access control lists through symlink traversal, potentially enabling unauthorized access or modification of sensitive files.

Such unauthorized manipulation of access controls and privilege escalation could lead to violations of security requirements mandated by common standards and regulations like GDPR and HIPAA, which require strict access controls and protection of sensitive data.

Therefore, if exploited, this vulnerability could negatively impact compliance by undermining the integrity and confidentiality of protected information.

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Detection Guidance

This vulnerability affects acl software versions prior to 2.4.0 and involves symlink traversal in libacl pathname-based functions. Detection involves verifying the installed acl version and checking for the presence of symbolic links in pathname components used by privileged processes.

To detect if your system is vulnerable, first check the installed acl version:

• acl --version

If the version is earlier than 2.4.0, your system is potentially vulnerable.

Next, to detect possible exploitation attempts or presence of malicious symbolic links in paths used by privileged processes, you can search for symbolic links in directories accessed by such processes. For example, to find symbolic links in a directory:

• find /path/to/important/directory -type l -ls

Additionally, monitoring system logs for unusual ACL manipulation or privilege escalation attempts may help detect exploitation.

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Impact Analysis

This vulnerability can have serious impacts by allowing local attackers to escalate their privileges on the affected system.

By exploiting the symlink traversal flaw, attackers can redirect ACL operations to arbitrary files or directories, enabling unauthorized modification of access control lists.

This unauthorized manipulation can compromise system security, potentially allowing attackers to gain higher-level access than intended and perform actions restricted to privileged users.

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Mitigation Strategies

To mitigate this vulnerability, you should upgrade acl to version 2.4.0 or later, as versions prior to 2.4.0 contain the symlink traversal flaw.

Additionally, restrict local user permissions to prevent attackers from controlling pathname components processed by privileged callers, thereby reducing the risk of unauthorized ACL manipulation.

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