CVE-2017-7358 in LightDM
Summary
by MITRE
In LightDM through 1.22.0, a directory traversal issue in debian/guest-account.sh allows local attackers to own arbitrary directory path locations and escalate privileges to root when the guest user logs out.
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Analysis
by VulDB Data Team • 08/24/2024
The vulnerability described in CVE-2017-7358 represents a critical directory traversal flaw within the LightDM display manager version 1.22.0 and earlier. This issue resides in the debian/guest-account.sh script which is part of the LightDM package distribution. The vulnerability specifically affects systems where LightDM is configured to provide guest user access functionality, creating a scenario where local attackers can exploit improper path handling to gain elevated privileges.
The technical exploitation of this vulnerability occurs through a directory traversal mechanism that allows attackers to manipulate file paths during guest user session cleanup operations. When a guest user logs out of the LightDM session, the guest-account.sh script executes with elevated privileges and processes directory paths without proper validation. This flaw enables attackers to specify arbitrary directory paths that the script will attempt to modify or remove, potentially leading to privilege escalation when the script executes with root permissions.
The operational impact of this vulnerability is severe as it provides local attackers with a straightforward path to root privilege escalation. Attackers can leverage this weakness to compromise the entire system by manipulating directory structures that the guest account cleanup process handles. The vulnerability is particularly dangerous because it requires no network access and can be exploited from within the system itself, making it difficult to detect through traditional network monitoring. The privilege escalation occurs during the logout process, which means that any user with access to the guest account can potentially exploit this vulnerability.
This vulnerability maps to CWE-22 Directory Traversal and aligns with ATT&CK technique T1068, which covers privilege escalation through local exploits. The flaw demonstrates poor input validation and improper privilege handling within system administration scripts. Organizations using LightDM with guest account functionality are particularly at risk, especially in multi-user environments where guest accounts are enabled. The vulnerability represents a classic example of insecure path manipulation in system-level scripts that execute with elevated privileges, creating a direct pathway for privilege escalation attacks.
Mitigation strategies for this vulnerability include upgrading to LightDM version 1.22.1 or later where the directory traversal issue has been patched. System administrators should disable guest account functionality if it is not required for their environment. Additionally, proper input validation and sanitization should be implemented in all system scripts that handle user-provided paths, particularly those that execute with elevated privileges. Regular security auditing of system scripts and privileged operations should be conducted to identify similar vulnerabilities. Organizations should also implement monitoring for unusual file system modifications during user session cleanup processes to detect potential exploitation attempts. The patch for this vulnerability specifically addresses the path traversal in the guest-account.sh script and ensures that directory operations are properly validated before execution.