CVE-2006-0055 in FreeBSD
Summary
by MITRE
The ispell_op function in ee on FreeBSD 4.10 to 6.0 uses predictable filenames and does not confirm which file is being written, which allows local users to overwrite arbitrary files via a symlink attack when ee invokes ispell.
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Analysis
by VulDB Data Team • 03/12/2021
The vulnerability identified as CVE-2006-0055 resides within the ispell_op function of the ee text editor on FreeBSD systems ranging from version 4.10 through 6.0. This flaw represents a classic file system race condition that exploits predictable filename generation and inadequate file validation mechanisms. The vulnerability occurs when the ee text editor invokes the ispell spell-checking utility, creating a scenario where local attackers can manipulate the file system to overwrite arbitrary files through symbolic link attacks. The root cause stems from the predictable naming scheme used by the ispell_op function, which generates filenames that attackers can anticipate and manipulate.
The technical implementation of this vulnerability involves a race condition where the ee editor creates temporary files with predictable names during the spell-checking process. When ispell is invoked, the system generates temporary files in a predictable manner that attackers can monitor and exploit. The function fails to validate the actual file being written to, instead relying on the predictable filename generation that allows attackers to create symbolic links to target files before the legitimate file operations occur. This type of vulnerability aligns with CWE-367, which describes the Time-of-Check to Time-of-Use (TOCTOU) race condition, where the state of a resource changes between the time it is checked and the time it is used.
The operational impact of this vulnerability is significant for local users who possess the ability to execute commands within the affected system's context. Attackers can leverage this weakness to overwrite critical system files, configuration files, or even files owned by other users, potentially leading to privilege escalation or system compromise. The attack requires minimal privileges and can be executed by any local user, making it particularly dangerous in multi-user environments where file system permissions may not adequately protect against such attacks. This vulnerability can be classified under the ATT&CK technique T1059.001 for Command and Scripting Interpreter, as attackers can use the compromised functionality to execute arbitrary commands through file overwrites.
Mitigation strategies for this vulnerability involve several approaches that address both the immediate security flaw and broader system protection measures. The most effective immediate solution is to update to FreeBSD versions that contain patches addressing this specific vulnerability, as the original issue was resolved through proper file validation and unpredictable temporary file naming. System administrators should also implement proper file system permissions and consider using more secure temporary file creation methods that avoid predictable naming schemes. Additionally, the principle of least privilege should be enforced to limit the ability of local users to create symbolic links in directories where sensitive operations occur. The vulnerability demonstrates the importance of implementing proper input validation and secure file handling practices, particularly in applications that interact with external utilities and create temporary files during their operation. Organizations should also consider implementing monitoring and alerting mechanisms to detect suspicious file system activities that might indicate exploitation attempts.