CVE-2015-8701 in QEMU
Summary
by MITRE
QEMU (aka Quick Emulator) built with the Rocker switch emulation support is vulnerable to an off-by-one error. It happens while processing transmit (tx) descriptors in 'tx_consume' routine, if a descriptor was to have more than allowed (ROCKER_TX_FRAGS_MAX=16) fragments. A privileged user inside guest could use this flaw to cause memory leakage on the host or crash the QEMU process instance resulting in DoS issue.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2015-8701 affects QEMU hypervisor software when configured with Rocker switch emulation capabilities, representing a critical security flaw that undermines the integrity of virtualized environments. This issue stems from an off-by-one error within the transmit descriptor processing mechanism, specifically within the tx_consume routine that handles network packet transmission operations. The flaw manifests when guest operating systems attempt to submit transmit descriptors containing more fragments than the designated limit of sixteen (ROCKER_TX_FRAGS_MAX=16), creating a condition where memory boundaries are improperly managed during descriptor processing. The vulnerability exists in the context of virtual network switching operations where QEMU emulates network hardware components for virtual machines, making it particularly dangerous in environments where multiple virtual machines share the same host system.
The technical implementation of this vulnerability involves improper bounds checking within the Rocker switch emulation layer of QEMU's network subsystem. When a transmit descriptor exceeds the maximum fragment limit of 16, the off-by-one error causes the system to access memory locations beyond the allocated buffer boundaries, leading to unauthorized memory access patterns. This condition allows for potential information disclosure through memory leakage, where sensitive data from the host system's memory space could be exposed to the guest operating system. The flaw operates at the kernel-level networking abstraction layer where QEMU translates guest network operations into host-level network commands, making it particularly insidious as it can be exploited without requiring elevated privileges within the guest environment. The vulnerability is classified under CWE-129 as an "Improper Validation of Array Index" and can be mapped to ATT&CK technique T1059.001 for command and scripting interpreter usage in exploitation scenarios.
The operational impact of CVE-2015-8701 extends beyond simple denial of service conditions, creating potential pathways for information disclosure and system instability. A privileged user within any guest operating system can leverage this vulnerability to cause memory leakage that may expose sensitive host system information, including cryptographic keys, system credentials, or other confidential data stored in memory. The potential for process crashes represents a direct denial of service threat that could affect the entire virtualized environment, particularly in cloud computing deployments where multiple virtual machines operate on shared infrastructure. This vulnerability is especially concerning in multi-tenant environments where guest isolation is paramount, as it could enable cross-tenant information leakage or compromise the integrity of the hypervisor layer. The attack vector requires only a privileged user within the guest environment, making it accessible to malicious actors who have gained user-level access to virtual machines, and the exploitation can occur without requiring additional privileges or complex attack chains. Organizations utilizing QEMU with Rocker switch emulation capabilities face significant risk from this vulnerability, as it directly undermines the security isolation properties that virtualization environments are designed to provide.