CVE-1999-0566 in AIX
Summary
by MITRE
An attacker can write to syslog files from any location, causing a denial of service by filling up the logs, and hiding activities.
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Analysis
by VulDB Data Team • 04/17/2026
This vulnerability represents a critical access control flaw in syslog file handling mechanisms that affects system logging functionality across multiple operating systems. The issue stems from insufficient permission checks during syslog file operations, allowing unauthorized users to write to system log files regardless of their privileges or the normal file access controls that should protect these critical system resources. The vulnerability exists at the kernel or system library level where syslog operations are processed, creating a pathway for malicious actors to manipulate log file contents without proper authentication or authorization. This weakness directly violates fundamental security principles of least privilege and proper access control enforcement, as it enables any user to inject data into system logs that should only be writable by system processes or authorized administrators.
The technical exploitation of this vulnerability involves leveraging the lack of proper file permission validation during syslog write operations. Attackers can craft malicious log entries that consume disk space rapidly, leading to system resource exhaustion and potential denial of service conditions. The vulnerability operates at the system call level where syslog functions are invoked, typically through standard logging libraries such as libc or system-specific implementations. This flaw can be triggered by any process or user that has access to the syslog interface, making it particularly dangerous as it requires minimal privileges to exploit. The implementation bypass occurs when the system fails to verify that the calling process has appropriate permissions to write to specific log files, allowing arbitrary writes to system logging destinations. This represents a classic example of improper privilege management where the system trusts the application layer without sufficient validation of underlying file access rights.
The operational impact of this vulnerability extends beyond simple denial of service to encompass significant security implications including log tampering and forensic data corruption. When attackers can write to syslog files from any location, they gain the ability to obscure their activities by either overwriting legitimate log entries or creating false entries that mislead security monitoring systems. This capability undermines the integrity of system audit trails and compromises the ability of security teams to perform effective incident response and forensics. The vulnerability can be exploited to create log flooding attacks that consume all available disk space, preventing legitimate logging operations and potentially causing system instability or crashes. Additionally, the ability to write to log files allows attackers to hide their presence by removing evidence of their activities or by creating misleading entries that mask their actual actions. This type of vulnerability directly impacts the availability and integrity of system logging services, which are fundamental to security monitoring and compliance requirements. The attack surface is particularly broad as it affects all systems that utilize standard syslog functionality, making it a widespread concern across enterprise environments.
Mitigation strategies for this vulnerability must address both immediate protection and long-term architectural improvements to system logging security. The primary solution involves implementing proper access controls and permission validation for syslog operations, ensuring that only authorized processes can write to system log files. System administrators should configure appropriate file permissions on syslog destinations and implement mandatory access controls that prevent unauthorized write access to logging directories. Regular security audits should verify that syslog configurations adhere to security best practices and that no unnecessary write permissions exist for log files. Network segmentation and monitoring should be implemented to detect anomalous log writing patterns that might indicate exploitation attempts. Additionally, organizations should implement log integrity monitoring solutions that can detect unauthorized modifications to log files and alert security teams to potential tampering. The implementation of secure logging practices, including proper log file ownership and permissions, should follow established security frameworks such as those outlined in the center for internet security cisc 20 controls. System updates and patches should be applied promptly to address known vulnerabilities in syslog implementations, and organizations should consider implementing additional logging security measures such as log file encryption and tamper detection mechanisms. This vulnerability highlights the importance of maintaining proper separation of privileges and ensuring that system services operate with the minimum necessary permissions to perform their functions, aligning with the principle of least privilege as defined in various security standards and frameworks including those referenced in the common weakness enumeration database.