CVE-2008-0217 in FreeBSD
Summary
by MITRE
The script program in FreeBSD 5.0 through 7.0-PRERELEASE invokes openpty, which creates a pseudo-terminal with world-readable and world-writable permissions when it is not run as root, which allows local users to read data from the terminal of the user running script.
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Analysis
by VulDB Data Team • 09/15/2018
The vulnerability described in CVE-2008-0217 represents a significant security flaw in the FreeBSD operating system's script command implementation. This issue affects versions from 5.0 through 7.0-PRERELEASE and stems from improper privilege handling during pseudo-terminal creation. The script command, which is commonly used to record terminal sessions, exhibits insecure default permissions when executed by non-root users. When the script program invokes the openpty system call, it creates a pseudo-terminal device file with overly permissive access controls that grant world-read and world-write permissions. This design flaw fundamentally undermines the security model of terminal session recording and creates a vector for privilege escalation and information disclosure attacks.
The technical implementation of this vulnerability occurs at the system call level where the openpty function fails to properly enforce privilege checks before creating the pseudo-terminal device. When a non-root user executes the script command, the underlying openpty implementation creates a pty device file with permissions that allow any user on the system to access the terminal session data. This behavior violates fundamental security principles of least privilege and proper access control enforcement. The vulnerability specifically relates to CWE-276, which addresses improper permissions for critical resources, and represents a classic case of insecure default permissions in system utilities. The flaw essentially creates a backdoor mechanism where local users can intercept and read terminal session data from other users who are running the script command.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks. An attacker with local access can exploit this weakness to capture sensitive information such as passwords, private keys, or other confidential data that users might input during terminal sessions. The vulnerability particularly affects environments where multiple users share the same system and where script is commonly used for session recording or automation tasks. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1056.001, which covers input injection through terminal session manipulation, and T1074, which involves data staging through local system access. The impact is significant because it allows for persistent monitoring of terminal sessions without requiring elevated privileges, making it particularly dangerous in multi-user environments or shared computing systems.
Mitigation strategies for this vulnerability should focus on immediate system updates and privilege enforcement mechanisms. The most effective solution involves upgrading to FreeBSD versions that have patched this vulnerability, as the original issue was resolved through proper permission handling in the openpty implementation. System administrators should also implement monitoring for script command usage and consider restricting access to the script utility through discretionary access control lists or file permissions. Additionally, organizations should review their terminal session recording practices and consider alternative secure session recording solutions that properly enforce privilege boundaries. The fix typically involves ensuring that pseudo-terminal device files are created with restrictive permissions that only allow the intended user to access them, preventing the world-readable and world-writable permissions that enabled this attack vector. Security hardening practices should include regular audit of system utilities and their permission settings to prevent similar issues from emerging in other components of the operating system.