CVE-2006-1624 in Linux
Summary
by MITRE
The default configuration of syslogd in the Linux sysklogd package does not enable the -x (disable name lookups) option, which allows remote attackers to cause a denial of service (traffic amplification) via messages with spoofed source IP addresses.
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Analysis
by VulDB Data Team • 04/13/2019
The vulnerability described in CVE-2006-1624 represents a significant security flaw in the default configuration of syslogd within the Linux sysklogd package that enables traffic amplification attacks. This issue stems from the absence of the -x command line option which would disable name lookups during syslog message processing. When syslogd receives messages with spoofed source IP addresses, it attempts to perform reverse DNS lookups on these addresses to resolve hostnames, creating a scenario where attackers can exploit this behavior to amplify network traffic volumes. The vulnerability is particularly concerning because it operates at the network infrastructure level, affecting systems that rely on standard syslog functionality for system monitoring and logging operations.
The technical flaw manifests when syslogd processes incoming messages without the -x flag, causing the daemon to perform DNS resolution requests for every message received. This behavior creates a traffic amplification effect where a small number of spoofed messages can trigger a much larger volume of DNS queries to external name servers. The amplification factor can be substantial, as each DNS lookup request may generate multiple responses, and the syslog daemon's processing of these messages can result in network traffic volumes that far exceed the original attack payload. This mechanism allows attackers to leverage legitimate system services to conduct denial of service attacks against target systems or networks, making it particularly dangerous in environments where network bandwidth is limited or where the target is already under stress.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential network saturation and resource exhaustion across multiple systems. When exploited, the vulnerability can cause significant network congestion as syslogd processes spoofed messages and generates DNS resolution requests that consume bandwidth and processing power. The attack can affect not only the targeted system but also upstream network infrastructure, as the amplified DNS traffic may overwhelm network links or upstream DNS servers. Additionally, the vulnerability can be particularly problematic in environments where syslog is used for security monitoring, as the amplification effect can obscure legitimate network activity and make it difficult to identify actual security incidents. Organizations may experience reduced system availability, degraded network performance, and potential service interruptions that can affect business operations and security monitoring capabilities.
Mitigation strategies for this vulnerability should focus on implementing proper syslogd configuration and network security controls. The primary recommendation is to always run syslogd with the -x flag to disable name lookups, which prevents the traffic amplification effect from occurring. Network administrators should also implement proper access controls and filtering mechanisms to prevent unauthorized access to syslog services, including configuring firewalls to restrict syslog traffic to trusted sources only. Additionally, organizations should consider implementing rate limiting on DNS queries and monitoring for unusual DNS traffic patterns that may indicate exploitation attempts. The vulnerability aligns with CWE-209, which addresses the improper handling of exceptions and errors, and relates to ATT&CK technique T1498, which covers network denial of service attacks through traffic amplification. Implementing these controls helps ensure that syslog services operate securely while maintaining their essential logging functionality for system monitoring and security operations.