CVE-2011-1490 in rsyslog
Summary
by MITRE
A memory leak in rsyslog before 5.7.6 was found in the way deamon processed log messages are logged when multiple rulesets were used and some output batches contained messages belonging to more than one ruleset. A local attacker could cause denial of the rsyslogd daemon service via a log message belonging to more than one ruleset
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Analysis
by VulDB Data Team • 02/02/2025
The vulnerability identified as CVE-2011-1490 represents a critical memory management flaw in the rsyslog daemon software that affected versions prior to 5.7.6. This memory leak occurred specifically within the daemon's processing logic when handling log messages under complex configuration scenarios involving multiple rulesets. The flaw manifested when the system encountered output batches containing messages that belonged to more than one ruleset simultaneously, creating a condition where allocated memory was not properly released back to the system.
The technical implementation of this vulnerability stems from improper memory deallocation within the rsyslog daemon's ruleset processing engine. When multiple rulesets were configured and log messages were processed through these overlapping configurations, the daemon failed to correctly manage memory references for messages that crossed ruleset boundaries. This resulted in progressive memory consumption that eventually led to system resource exhaustion and daemon termination. The vulnerability was particularly insidious because it required specific conditions to be triggered, namely the simultaneous use of multiple rulesets and the processing of messages that belonged to more than one ruleset within the same output batch.
From an operational perspective, this vulnerability created a significant denial of service risk for systems relying on rsyslog for centralized logging operations. A local attacker with minimal privileges could exploit this flaw by crafting specially formatted log messages that would trigger the memory leak condition. The impact extended beyond simple service disruption as the daemon would eventually crash or become unresponsive, leading to loss of syslog functionality and potential data loss during the recovery process. Organizations using complex logging configurations with multiple rulesets were particularly vulnerable to this attack vector, as the conditions necessary for exploitation were more likely to occur in production environments with sophisticated logging requirements.
The vulnerability aligns with CWE-401, which addresses improper management of memory allocation and deallocation, specifically focusing on memory leaks that occur when resources are not properly released. From an adversarial perspective, this flaw fits within the ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion, though in this case the resource exhaustion occurred at the local daemon level rather than network infrastructure. The exploitability of this vulnerability was enhanced by the fact that it required no elevated privileges beyond local access, making it particularly dangerous in multi-user environments where attackers might have limited but persistent access to the system. Organizations implementing robust patch management policies were able to mitigate this vulnerability by upgrading to rsyslog version 5.7.6 or later, which included proper memory management fixes for ruleset processing scenarios. The incident highlighted the importance of thorough testing of logging configurations under realistic conditions and demonstrated how seemingly benign configuration elements could create exploitable conditions in system components.