CVE-2011-4539 in dhcp
Summary
by MITRE
dhcpd in ISC DHCP 4.x before 4.2.3-P1 and 4.1-ESV before 4.1-ESV-R4 does not properly handle regular expressions in dhcpd.conf, which allows remote attackers to cause a denial of service (daemon crash) via a crafted request packet.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability identified as CVE-2011-4539 represents a critical denial of service flaw within the Internet Systems Consortiums DHCP daemon implementation. This issue affects multiple versions of the ISC DHCP server software, specifically those in the 4.x release series prior to 4.2.3-P1 and the 4.1-ESV series before 4.1-ESV-R4. The flaw manifests in the daemon's handling of regular expressions within the dhcpd.conf configuration file, creating a scenario where malicious actors can exploit this weakness to crash the DHCP service and disrupt network operations.
The technical root cause of this vulnerability lies in improper input validation and processing of regular expression patterns within the DHCP configuration file. When the dhcpd daemon encounters specially crafted regular expressions in the dhcpd.conf file, it fails to properly sanitize or validate these patterns before processing them. This inadequate handling allows attackers to submit malformed request packets that trigger buffer overflows or other memory corruption conditions within the daemon's regular expression evaluation engine. The vulnerability specifically targets the configuration parsing mechanism rather than the network protocol itself, making it particularly insidious as it can be exploited through legitimate network traffic.
From an operational standpoint, this vulnerability poses significant risks to network infrastructure stability and availability. The denial of service condition can result in complete disruption of DHCP services across affected networks, forcing network administrators to manually restart the dhcpd daemon and potentially causing temporary network outages. The attack vector is particularly concerning because it requires only remote access to submit malicious packets, making it accessible to anyone who can communicate with the DHCP server over the network. This vulnerability directly impacts network infrastructure reliability and can be exploited to create persistent service disruptions that may go unnoticed for extended periods, especially in large enterprise environments where DHCP services are critical for network operations.
The impact of this vulnerability aligns with CWE-129, which describes improper validation of input boundaries, and can be mapped to ATT&CK technique T1499.1 for network denial of service attacks. Network administrators should prioritize patching affected systems to address this vulnerability, as the fix involves proper input validation and sanitization of regular expression patterns within the dhcpd.conf file. Organizations should also implement network monitoring solutions to detect anomalous DHCP traffic patterns that might indicate exploitation attempts. Additionally, configuration management practices should include regular review of dhcpd.conf files to ensure that regular expressions are properly validated and that only authorized patterns are included in production configurations. The vulnerability demonstrates the importance of robust input validation in server applications and highlights the critical need for proper security testing of configuration file parsing mechanisms.