CVE-2011-4623 in rsyslog
Summary
by MITRE
Integer overflow in the rsCStrExtendBuf function in runtime/stringbuf.c in the imfile module in rsyslog 4.x before 4.6.6, 5.x before 5.7.4, and 6.x before 6.1.4 allows local users to cause a denial of service (daemon hang) via a large file, which triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 01/05/2025
The vulnerability identified as CVE-2011-4623 represents a critical integer overflow flaw within the rsyslog daemon's imfile module that affects multiple versions of the rsyslog logging system. This issue resides in the rsCStrExtendBuf function located in runtime/stringbuf.c, specifically within the imfile module responsible for processing file-based log data. The vulnerability manifests when rsyslog processes large files, creating a condition where integer arithmetic operations exceed the maximum representable value for signed integers, leading to unexpected behavior in memory allocation and buffer management.
The technical implementation of this vulnerability exploits the fundamental flaw in how integer values are handled during buffer extension operations. When rsyslog encounters a large file, the rsCStrExtendBuf function attempts to calculate new buffer sizes based on file dimensions and existing buffer states. The integer overflow occurs during these calculations, causing the system to allocate insufficient memory or incorrectly sized buffers. This heap-based buffer overflow results in daemon instability and ultimately leads to a denial of service condition where the rsyslog daemon becomes unresponsive or enters an infinite loop. The vulnerability is particularly dangerous because it operates at the core level of log processing, where the daemon's ability to receive and process system logs is fundamentally compromised.
The operational impact of CVE-2011-4623 extends beyond simple service disruption, as it can severely compromise system security and monitoring capabilities. When the rsyslog daemon hangs due to this vulnerability, system administrators lose critical log data collection and forwarding functionality, potentially creating blind spots in security monitoring and incident response procedures. The vulnerability affects systems where rsyslog is used as the primary logging daemon, which includes virtually all modern linux distributions and many network appliances that rely on syslog for event logging. Attackers can exploit this weakness by creating or manipulating large log files that trigger the overflow condition, effectively disabling the logging infrastructure and potentially masking malicious activities. This vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions, and demonstrates how such flaws can be leveraged to achieve persistent denial of service against critical system services.
Mitigation strategies for CVE-2011-4623 require immediate patching of affected rsyslog installations to versions 4.6.6, 5.7.4, or 6.1.4, respectively. Organizations should implement comprehensive monitoring to detect unusual file sizes or processing patterns that might indicate exploitation attempts. Security teams should also consider implementing file size limits or rotation policies for log files processed by rsyslog to prevent the triggering of buffer overflow conditions. The ATT&CK framework categorizes this vulnerability under T1499.004, which covers network denial of service attacks, and T1562.001, which addresses disabling services. System administrators should also consider implementing intrusion detection systems that can monitor for suspicious file processing patterns and establish baseline behaviors for log file handling to identify potential exploitation attempts. Regular security audits of logging infrastructure and proper input validation practices should be enforced to prevent similar vulnerabilities from emerging in other system components.