CVE-2013-4129 in Linux
Summary
by MITRE
The bridge multicast implementation in the Linux kernel through 3.10.3 does not check whether a certain timer is armed before modifying the timeout value of that timer, which allows local users to cause a denial of service (BUG and system crash) via vectors involving the shutdown of a KVM virtual machine, related to net/bridge/br_mdb.c and net/bridge/br_multicast.c.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/06/2017
The vulnerability identified as CVE-2013-4129 represents a critical flaw in the Linux kernel's bridge multicast implementation that affects versions through 3.10.3. This issue specifically resides within the networking subsystem of the kernel, particularly in the bridge multicast database management components. The vulnerability stems from improper timer management within the multicast bridge functionality, creating a scenario where a local attacker can manipulate system resources to trigger unintended behavior. The flaw manifests when the kernel attempts to modify timeout values for timers without first verifying whether these timers are properly armed, leading to potential system instability and complete system crashes.
The technical nature of this vulnerability places it squarely within CWE-665, which addresses improper initialization of resources, specifically timer management in this context. The flaw exists in the net/bridge/br_mdb.c and net/bridge/br_multicast.c source files, indicating that the issue affects the multicast database and multicast forwarding mechanisms within the kernel's bridge implementation. When a KVM virtual machine undergoes shutdown operations, the affected code path becomes triggered, allowing malicious local processes to exploit the timer handling inconsistency. The vulnerability is classified as a local privilege escalation vector since it requires local access but can result in system-wide denial of service conditions that compromise system availability.
The operational impact of this vulnerability extends beyond simple system crashes to encompass broader security implications for virtualized environments. When exploited, the vulnerability can cause the entire kernel to BUG and crash, effectively rendering the affected system unusable until manual reboot occurs. In virtualized environments running KVM, this vulnerability poses significant risks as it can be leveraged by malicious processes running within guest operating systems to target the host system. The vulnerability's exploitation requires local access but can result in system-wide availability disruption, making it particularly dangerous in multi-tenant environments where guest isolation is paramount. Attackers can repeatedly trigger the timer modification sequence to maintain persistent denial of service conditions.
Mitigation strategies for this vulnerability center around kernel updates and patching procedures. The most effective remediation involves upgrading to Linux kernel versions beyond 3.10.3 where the timer management logic has been corrected to properly check timer state before modification. System administrators should prioritize patching operations, particularly in environments running KVM virtualization where the vulnerability can be exploited to target host systems. Additional defensive measures include implementing proper access controls to limit local user privileges, monitoring for abnormal system behavior, and maintaining robust backup and recovery procedures. The vulnerability also highlights the importance of proper resource management in kernel space, where timer handling and resource cleanup must be carefully validated to prevent similar issues from manifesting in other subsystems. Organizations should also consider implementing network segmentation and monitoring to detect potential exploitation attempts and maintain compliance with security standards that require proper kernel resource management practices.