CVE-2002-0542 in OpenBSD
Summary
by MITRE
mail in OpenBSD 2.9 and 3.0 processes a tilde (~) escape character in a message even when it is not in interactive mode, which could allow local users to gain root privileges via calls to mail in cron.
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Analysis
by VulDB Data Team • 12/30/2024
The vulnerability described in CVE-2002-0542 represents a critical privilege escalation flaw within the mail utility of OpenBSD versions 2.9 and 3.0. This issue arises from improper handling of the tilde (~) escape character in non-interactive modes, creating an avenue for local attackers to execute arbitrary commands with elevated privileges. The flaw specifically manifests when the mail command is invoked through cron jobs, which typically run with root privileges, thereby amplifying the potential impact of the vulnerability.
The technical root cause of this vulnerability lies in the mail utility's failure to properly sanitize input when processing the tilde character outside of interactive sessions. In interactive mode, the tilde character typically functions as a home directory reference, but in non-interactive contexts, the mail command should not interpret such escape sequences. However, the flawed implementation allows the tilde to be processed as a command invocation, enabling attackers to craft malicious mail messages that contain tilde escape sequences. This behavior violates the principle of least privilege and creates a direct path for privilege escalation.
When the mail command executes within a cron job context, the vulnerability becomes particularly dangerous because cron jobs often run with root privileges. An attacker who can influence the content of a mail message or control the mail delivery process can exploit this flaw to execute arbitrary commands as the root user. The operational impact extends beyond simple privilege escalation, as it can enable attackers to modify system files, install backdoors, or completely compromise the affected system. This vulnerability directly maps to CWE-78, which describes improper neutralization of special elements used in OS commands, and CWE-20, which covers input validation issues that can lead to command injection.
The attack vector for this vulnerability is particularly insidious because it leverages legitimate system functionality to achieve malicious objectives. Attackers can place specially crafted mail messages containing tilde escape sequences into the mail spool or delivery queue, which are then processed by the mail utility when cron jobs execute. The attack requires local access to the system but can be executed without requiring authentication, making it a significant concern for systems where local users might have access to mail functionality. The vulnerability's persistence in OpenBSD versions 2.9 and 3.0 demonstrates a failure in proper privilege separation and input validation mechanisms.
Mitigation strategies for CVE-2002-0542 should focus on immediate patching of affected OpenBSD versions, as the vulnerability represents a fundamental flaw in the mail utility's command processing. Organizations should ensure that all systems running OpenBSD 2.9 or 3.0 are updated to patched versions that properly handle tilde escape sequences in non-interactive contexts. Additionally, administrators should implement strict access controls on mail spool directories and monitor for unauthorized mail delivery attempts. The fix should address the core issue by ensuring that escape character processing is disabled in non-interactive modes, aligning with ATT&CK technique T1059.001 for command and scripting interpreter usage. System hardening measures should also include restricting cron job execution privileges and implementing proper input validation for all mail processing functions to prevent similar issues in other system components.