Source: secalert@redhat.com
Memory leak in hw/9pfs/9p.c in QEMU (aka Quick Emulator) allows local privileged guest OS users to cause a denial of service (host memory consumption and possibly QEMU process crash) by leveraging a missing cleanup operation in FileOperations.
CVE-2016-9914 presents a critical memory leak vulnerability in QEMU's 9p filesystem implementation, allowing a malicious guest OS user to exhaust the host's memory resources, leading to a denial-of-service (DoS) condition and potentially a QEMU process crash. This vulnerability can be exploited by a local attacker with guest OS privileges to severely impact the availability of the virtualized environment.
Step 1: Guest OS Access: The attacker gains privileged access within the guest operating system. This could be achieved through other vulnerabilities or legitimate means, such as a compromised user account.
Step 2: 9p Filesystem Interaction: The attacker interacts with the 9p filesystem, typically by mounting a 9p share from the host. This establishes a communication channel between the guest and the host's QEMU instance.
Step 3: Triggering the Memory Leak: The attacker performs a series of file operations (e.g., opening, closing, or manipulating files) within the 9p filesystem in a specific sequence that exploits the missing cleanup operation. This causes memory to be allocated on the host without being freed.
Step 4: Memory Exhaustion: Repeated execution of Step 3 leads to a gradual but continuous increase in memory consumption on the host machine.
Step 5: Denial of Service: Eventually, the host's memory is exhausted, leading to performance degradation, system instability, and potentially a crash of the QEMU process, resulting in a DoS condition for all running virtual machines.
The root cause lies in a missing cleanup operation within the FileOperations structure in hw/9pfs/9p.c. Specifically, when a guest OS interacts with the 9p filesystem, certain file operations allocate memory. Due to the lack of proper deallocation in the event of errors or specific file operation sequences, this allocated memory is never freed. Over time, repeated exploitation of this flaw leads to a gradual but persistent memory leak on the host machine. This memory exhaustion eventually leads to a DoS condition, impacting the host's performance and potentially crashing the QEMU process. The vulnerability is triggered by specific interactions with the 9p filesystem, such as opening, closing, or manipulating files in a way that triggers the memory allocation without the corresponding deallocation.
There is no specific APT group or malware family known to be actively exploiting this vulnerability. However, any threat actor targeting virtualized environments could potentially leverage this vulnerability for a DoS attack. CISA KEV status: Not Listed.
Monitor host memory usage for abnormal and sustained increases, especially when 9p filesystem shares are in use.
Analyze QEMU process memory consumption over time. A steady increase in memory usage indicates a potential leak.
Examine QEMU logs for errors or warnings related to the 9p filesystem, file operations, or memory allocation.
Implement host-based intrusion detection systems (HIDS) to monitor for suspicious file operations within the 9p filesystem.
Network traffic analysis can identify unusual patterns of 9p filesystem communication between the guest and host.
Upgrade QEMU to a patched version that addresses CVE-2016-9914. This is the most effective remediation.
If upgrading is not immediately possible, disable the 9p filesystem if it is not required. This eliminates the attack surface.
Limit the resources allocated to each virtual machine to prevent a single VM from consuming all available host memory.
Implement host-based monitoring and alerting to detect and respond to unusual memory consumption patterns.
Regularly audit and patch the host operating system and QEMU installation.
Implement strong access controls within the guest OS to limit the privileges of users who can interact with the 9p filesystem.