CVE-2008-5618 in rsyslog
Summary
by MITRE
imudp in rsyslog 4.x before 4.1.2, 3.21 before 3.21.9 beta, and 3.20 before 3.20.2 generates a message even when it is sent by an unauthorized sender, which allows remote attackers to cause a denial of service (disk consumption) via a large number of spurious messages.
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Analysis
by VulDB Data Team • 05/29/2025
The vulnerability identified as CVE-2008-5618 affects the imudp module within rsyslog versions prior to specific patches, representing a significant security flaw that undermines the integrity and availability of syslog processing systems. This issue specifically impacts rsyslog versions 4.x before 4.1.2, 3.21 before 3.21.9 beta, and 3.20 before 3.20.2, where the imudp input module fails to properly validate message sources, creating a condition that allows unauthorized senders to inject malicious data into the logging infrastructure.
The technical flaw resides in the imudp module's inability to effectively authenticate or filter incoming UDP messages based on their source legitimacy. When rsyslog receives UDP messages through the imudp interface, it processes and logs these messages without adequate verification of the sender's authorization status. This weakness creates a scenario where remote attackers can exploit the system by sending large volumes of spoofed or unauthorized UDP messages to the rsyslog daemon, causing it to log these spurious entries without proper filtering mechanisms in place.
The operational impact of this vulnerability manifests as a potential denial of service condition that specifically targets disk space consumption within the affected systems. As attackers flood the rsyslog daemon with numerous unauthorized messages, the system's disk storage becomes rapidly consumed, leading to performance degradation or complete system unavailability. This resource exhaustion attack effectively prevents legitimate logging operations from functioning properly, as the storage space allocated for log files becomes saturated with worthless data generated by malicious actors. The vulnerability particularly affects systems where rsyslog is configured to accept UDP messages from untrusted networks, making it a critical concern for organizations with exposed logging infrastructure.
The security implications of this vulnerability align with CWE-20, which describes improper input validation, and can be categorized under ATT&CK technique T1499.2, which involves resource exhaustion attacks targeting disk space. Organizations utilizing vulnerable rsyslog versions face significant risk of operational disruption, as the denial of service condition can persist until manual intervention occurs to clear disk space or restart the logging service. The vulnerability demonstrates how seemingly minor configuration flaws in system components can lead to substantial operational impacts, particularly when combined with the widespread use of rsyslog across enterprise environments.
Mitigation strategies for this vulnerability involve immediate deployment of patched rsyslog versions that include proper message validation and filtering mechanisms within the imudp module. System administrators should implement network-level access controls to restrict UDP traffic to rsyslog ports, particularly when running on public interfaces. Additionally, configuring rsyslog with proper authentication mechanisms and limiting the scope of trusted sources for UDP messages provides defense-in-depth protection. Organizations should also establish monitoring procedures to detect unusual disk consumption patterns that may indicate exploitation attempts, and implement automated alerting systems to respond quickly to potential resource exhaustion attacks targeting their logging infrastructure.