CVE-2011-1951 in syslog-ng
Summary
by MITRE
lib/logmatcher.c in Balabit syslog-ng before 3.2.4, when the global flag is set and when using PCRE 8.12 and possibly other versions, allows remote attackers to cause a denial of service (memory consumption) via a message that does not match a regular expression.
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Analysis
by VulDB Data Team • 11/14/2021
The vulnerability identified as CVE-2011-1951 affects the syslog-ng system logging daemon developed by Balabit, specifically impacting versions prior to 3.2.4. This issue resides within the lib/logmatcher.c component of the software and represents a denial of service weakness that can be exploited remotely by attackers. The vulnerability manifests when the global flag is enabled in regular expression processing and when utilizing PCRE version 8.12 or potentially other versions of the Perl Compatible Regular Expressions library. The core technical flaw involves the improper handling of regular expression matching when a message fails to match the specified pattern, leading to excessive memory consumption that can ultimately result in system resource exhaustion.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged by remote attackers to consume system resources continuously until the affected syslog-ng process becomes unresponsive or crashes entirely. When the global flag is enabled in PCRE processing, the regular expression engine may enter into inefficient memory allocation patterns when processing non-matching messages, creating a condition where memory consumption grows exponentially or remains allocated indefinitely. This behavior particularly affects systems that rely heavily on syslog-ng for log processing and that have not implemented proper input validation or rate limiting mechanisms. The vulnerability demonstrates a classic example of resource exhaustion attacks that can be amplified through repeated malicious message submissions.
From a cybersecurity perspective, this vulnerability aligns with CWE-400, which categorizes improper handling of regular expressions as a weakness leading to resource consumption issues. The attack pattern follows typical denial of service methodologies described in the MITRE ATT&CK framework under the T1499 category for resource exhaustion attacks. Organizations utilizing syslog-ng in production environments should consider this vulnerability as part of their broader security posture assessment, particularly in environments where syslog-ng serves as a central logging aggregation point. The vulnerability also highlights the importance of proper input validation and the need for robust error handling in regular expression processing components, as the issue stems from inadequate handling of edge cases in pattern matching operations.
Mitigation strategies for CVE-2011-1951 primarily involve upgrading to syslog-ng version 3.2.4 or later, which includes patches addressing the improper regular expression handling behavior. System administrators should also implement rate limiting and input validation measures to prevent malicious message flooding, while monitoring for unusual memory consumption patterns in syslog-ng processes. Additionally, organizations should consider implementing network segmentation and access controls to limit exposure of syslog-ng instances to untrusted networks, as the vulnerability requires remote network access to exploit. The fix implemented in version 3.2.4 specifically addresses the memory allocation behavior when processing non-matching regular expressions, ensuring that system resources are properly released regardless of match outcomes.