Source: secalert@redhat.com
Memory leak in hw/9pfs/9p-proxy.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 the proxy backend.
QEMU, a widely used virtualization platform, is vulnerable to a memory leak that can be triggered by a guest OS. This vulnerability allows a malicious guest to exhaust the host's memory, potentially leading to a denial-of-service (DoS) condition and a possible QEMU process crash, severely impacting system availability.
Step 1: Guest Interaction: A privileged user within the guest OS initiates interactions with the 9p filesystem, which is configured to use the proxy backend.
Step 2: Proxy Backend Allocation: The 9p proxy backend in QEMU allocates memory on the host to handle the guest's filesystem requests.
Step 3: Missing Cleanup: After processing the request, the allocated memory is not properly freed or deallocated by the proxy backend.
Step 4: Repeated Requests: The guest user repeatedly sends requests to the 9p filesystem, triggering the memory allocation process again and again.
Step 5: Memory Exhaustion: With each request, more memory is allocated on the host, leading to a gradual increase in memory consumption. The memory leak eventually exhausts the host's available memory.
Step 6: Denial of Service: The host runs out of memory, potentially leading to a denial-of-service condition, including system instability and a possible QEMU process crash.
The vulnerability resides in hw/9pfs/9p-proxy.c within QEMU's 9p filesystem proxy. The root cause is a missing cleanup operation within the proxy backend. When a guest OS interacts with the 9p filesystem, the proxy backend allocates memory to handle the requests. Due to the missing cleanup, this allocated memory is not freed after use. Repeated interactions with the 9p filesystem from the guest OS lead to a continuous accumulation of allocated memory on the host, eventually leading to host memory exhaustion. This memory leak can eventually cause the QEMU process to crash, resulting in a denial-of-service. The flaw is a resource exhaustion vulnerability, specifically a memory leak, stemming from improper memory management within the 9p proxy implementation. The lack of proper deallocation of resources after use is the core issue.
While specific APT attribution is difficult to confirm without further investigation, vulnerabilities like this are often exploited by various threat actors. This type of vulnerability is attractive to actors looking for denial-of-service capabilities. This vulnerability is not listed on the CISA KEV at the time of this report.
Monitor host memory usage, specifically the QEMU process's memory consumption. A steadily increasing memory footprint over time is a strong indicator.
Analyze QEMU logs for errors related to memory allocation or filesystem operations, particularly those involving the 9p filesystem.
Implement host-based intrusion detection systems (HIDS) to monitor for unusual process behavior, such as excessive memory allocation by QEMU.
Network traffic analysis: Monitor network traffic associated with the 9p filesystem (typically over TCP). Anomalous patterns of high volume or frequent requests could indicate exploitation.
Examine the guest OS for suspicious activity related to file access and filesystem operations, especially if performed by a privileged user.
Update QEMU to a patched version that addresses CVE-2016-9916. Ensure that the fix is applied to all affected QEMU instances.
Implement resource limits on the QEMU process to prevent it from consuming all available host memory. This can mitigate the impact of the memory leak.
Restrict guest OS access to the 9p filesystem, especially for untrusted guests. Consider removing the 9p filesystem support if it is not required.
Regularly monitor host memory usage and QEMU process behavior to detect any anomalous activity.
Implement a host-based intrusion detection system (HIDS) to monitor for unusual process behavior, such as excessive memory allocation by QEMU.
Consider using memory management tools and techniques, such as memory profiling, to identify and address memory leaks in QEMU.