Multiple buffer overflows in ISC DHCP Distribution server (dhcpd) 1.0 and 2.0 allow a remote attacker to cause a denial of service (crash) and possibly execute arbitrary commands via long options.
Remote attackers can exploit multiple buffer overflows in older versions of the ISC DHCP server to cause a denial-of-service (DoS) or potentially achieve remote code execution (RCE). This vulnerability, stemming from insufficient input validation of DHCP option lengths, allows attackers to inject malicious data, leading to a crash or system compromise. Organizations running vulnerable DHCP servers are at significant risk and should prioritize patching or mitigation.
Step 1: Target Identification: The attacker identifies a target network segment or a specific IP address range served by a vulnerable ISC DHCP server (dhcpd 1.0 or 2.0).
Step 2: Packet Crafting: The attacker crafts a malicious DHCP packet. This packet includes a DHCP option with a crafted length field and a payload designed to overflow a buffer within the dhcpd process.
Step 3: Packet Delivery: The attacker sends the malicious DHCP packet to the target DHCP server. This can be achieved through various methods, including direct network access or by poisoning the network with a rogue DHCP server.
Step 4: Vulnerability Trigger: The DHCP server receives the malicious packet and attempts to process the crafted option. Due to the lack of bounds checking on the option length, the server copies the attacker-controlled data into a buffer that is too small.
Step 5: Buffer Overflow: The buffer overflow occurs, overwriting adjacent memory regions. This can overwrite critical data structures, function pointers, or other sensitive information.
Step 6: Exploitation (DoS/RCE): The overwritten data can lead to a denial-of-service (DoS) by crashing the dhcpd process. Alternatively, if the attacker can control the overwritten data, they may be able to redirect the program flow to execute arbitrary code, achieving remote code execution (RCE).
Root Cause: The vulnerability lies within the ISC DHCP server (dhcpd) versions 1.0 and 2.0, specifically in how it handles DHCP options. The server fails to properly validate the length of option data received in DHCP packets. This allows an attacker to send a DHCP packet with an option containing a length value larger than the allocated buffer. This leads to a buffer overflow, where the attacker-controlled data overwrites adjacent memory regions. This can lead to a crash (DoS) or, with careful crafting of the malicious option, potentially allow for the execution of arbitrary code, granting the attacker control over the server. The lack of bounds checking on option lengths is the fundamental flaw.