CVE-2011-0997 in DHCP
Summary
by MITRE
dhclient in ISC DHCP 3.0.x through 4.2.x before 4.2.1-P1, 3.1-ESV before 3.1-ESV-R1, and 4.1-ESV before 4.1-ESV-R2 allows remote attackers to execute arbitrary commands via shell metacharacters in a hostname obtained from a DHCP message, as demonstrated by a hostname that is provided to dhclient-script.
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Analysis
by VulDB Data Team • 12/08/2024
The vulnerability identified as CVE-2011-0997 represents a critical command injection flaw in the ISC DHCP client software family affecting versions 3.0.x through 4.2.x before 4.2.1-P1 and specific ESV releases. This vulnerability resides in the dhclient component which processes DHCP messages and subsequently executes shell commands through the dhclient-script mechanism. The flaw occurs when the DHCP client receives a hostname parameter from a malicious DHCP server that contains shell metacharacters, creating an environment where arbitrary code execution becomes possible. The vulnerability specifically targets the processing of hostname data within DHCP messages without proper sanitization of shell metacharacters, allowing attackers to inject malicious commands that get executed in the context of the dhclient process.
The technical implementation of this vulnerability stems from improper input validation and sanitization within the DHCP client's hostname handling logic. When dhclient receives a DHCP offer or ack message containing a hostname field, it passes this data directly to the dhclient-script without adequate escaping or filtering of special shell characters such as semicolons, ampersands, pipes, and backticks. This design flaw aligns with CWE-78, which specifically addresses improper neutralization of special elements used in shell commands, making it a direct instance of shell injection vulnerability. The attack vector is particularly dangerous because it requires no authentication or privileged access on the target system, as the vulnerability is triggered simply by receiving a malicious DHCP response from a compromised or malicious DHCP server.
The operational impact of this vulnerability extends across numerous network environments where ISC DHCP clients are deployed, including enterprise networks, home routers, and various network infrastructure devices that rely on DHCP for IP address allocation. An attacker positioned within the same network segment can easily exploit this vulnerability by setting up a rogue DHCP server that responds to DHCP requests with malicious hostnames containing shell commands. The consequences include complete system compromise, allowing attackers to execute arbitrary code with the privileges of the dhclient process, which typically runs with elevated permissions on many systems. This vulnerability can be leveraged for privilege escalation, data exfiltration, network reconnaissance, and persistence mechanisms, making it particularly attractive to threat actors. The attack scenario is consistent with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1068 for Exploitation for Privilege Escalation.
Mitigation strategies for CVE-2011-0997 require immediate patching of affected ISC DHCP client versions to the latest stable releases, specifically ensuring that systems are updated to versions 4.2.1-P1 or later for the 4.2.x series, and appropriate ESV releases for the 3.1 and 4.1 series. Network administrators should implement DHCP snooping mechanisms to prevent unauthorized DHCP servers from operating within the network, as this provides an additional layer of defense against rogue DHCP servers. Additionally, configuring firewalls to restrict DHCP traffic between trusted and untrusted networks can limit the attack surface. System administrators should also consider implementing network segmentation and monitoring to detect unusual DHCP activity patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of input validation and sanitization in network protocols, particularly in components that interact with shell environments, and highlights the necessity of maintaining up-to-date security patches across all network infrastructure components.