CVE-2009-1893 in dhcp
Summary
by MITRE
The configtest function in the Red Hat dhcpd init script for DHCP 3.0.1 in Red Hat Enterprise Linux (RHEL) 3 allows local users to overwrite arbitrary files via a symlink attack on an unspecified temporary file, related to the "dhcpd -t" command.
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Analysis
by VulDB Data Team • 08/12/2021
The vulnerability identified as CVE-2009-1893 resides within the Red Hat dhcpd init script implementation for DHCP version 3.0.1 running on Red Hat Enterprise Linux 3 systems. This issue represents a classic symlink attack scenario that exploits improper handling of temporary files during the configuration testing process. The vulnerability specifically affects the configtest function within the init script, which executes the dhcpd -t command to validate DHCP server configurations before deployment. When local users can manipulate the symbolic link structure, they gain the ability to overwrite arbitrary files on the system, creating a significant privilege escalation vector.
The technical flaw manifests through the insecure creation and handling of temporary files during the dhcpd configuration testing phase. The init script does not properly validate or secure temporary file creation processes, allowing attackers to establish symbolic links that redirect file operations to unintended destinations. This weakness stems from the predictable naming conventions and lack of proper file permission controls when temporary files are created. The vulnerability is classified under CWE-377 as insecure temporary file handling and aligns with CWE-367 which addresses inadequate privilege separation. Attackers can exploit this by creating malicious symbolic links in directories where the init script expects temporary files to be created, thereby gaining write access to files that should remain protected.
The operational impact of this vulnerability extends beyond simple file overwrites, as it provides local users with a method to escalate privileges and potentially compromise the entire system. Since the dhcpd service typically runs with elevated privileges, successful exploitation can result in unauthorized modification of critical system files, configuration files, or even the replacement of executables with malicious counterparts. This creates a persistent threat vector that could allow attackers to maintain access or establish backdoors within the network infrastructure. The attack requires local system access but offers significant privileges, making it particularly dangerous in multi-user environments where privilege separation is crucial for maintaining security boundaries.
Mitigation strategies for CVE-2009-1893 focus on addressing the underlying file handling vulnerabilities within the init script and implementing proper privilege separation measures. System administrators should immediately apply the vendor-provided security patches that fix the temporary file creation logic in the dhcpd init script. Additionally, implementing proper file permission controls and using secure temporary file creation methods such as mkstemp or similar functions can prevent symlink attacks. The solution should also include monitoring for suspicious file creation patterns and implementing discretionary access controls that prevent unauthorized symbolic link creation in critical system directories. Organizations should follow ATT&CK technique T1068 which addresses privilege escalation through local exploitation, and ensure proper system hardening practices are implemented to prevent similar vulnerabilities in other services. Regular security audits of init scripts and system configuration files should be conducted to identify and remediate similar insecure temporary file handling patterns that could lead to privilege escalation attacks.