CVE-2018-15471 in Xen
Summary
by MITRE
An issue was discovered in xenvif_set_hash_mapping in drivers/net/xen-netback/hash.c in the Linux kernel through 4.18.1, as used in Xen through 4.11.x and other products. The Linux netback driver allows frontends to control mapping of requests to request queues. When processing a request to set or change this mapping, some input validation (e.g., for an integer overflow) was missing or flawed, leading to OOB access in hash handling. A malicious or buggy frontend may cause the (usually privileged) backend to make out of bounds memory accesses, potentially resulting in one or more of privilege escalation, Denial of Service (DoS), or information leaks.
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Analysis
by VulDB Data Team • 05/02/2023
The vulnerability described in CVE-2018-15471 represents a critical flaw in the Linux kernel's Xen netback driver component that enables unauthorized privilege escalation and system compromise through improper input validation. This issue exists in the xenvif_set_hash_mapping function within drivers/net/xen-netback/hash.c, affecting Linux kernel versions up to 4.18.1 and Xen hypervisor versions through 4.11.x. The vulnerability stems from inadequate validation of integer values used in hash mapping operations, creating a path for malicious frontends to manipulate the backend driver's memory access patterns. The flaw specifically manifests when the driver processes requests to set or modify request queue mappings, where the absence of proper bounds checking allows for out-of-bounds memory accesses that can be exploited by unprivileged frontend components.
The technical implementation of this vulnerability involves a classic integer overflow condition that occurs during hash mapping operations within the Xen virtualization environment. When a frontend attempts to configure hash mappings for network packet processing, the backend driver fails to validate the input parameters properly, particularly regarding the size and range of values used in memory allocation calculations. This validation failure creates a scenario where an attacker-controlled value can cause arithmetic overflow or underflow conditions, resulting in memory addresses that extend beyond the allocated buffer boundaries. The vulnerability is classified under CWE-129 as "Improper Validation of Array Index" and falls under the broader category of CWE-191 as "Integer Underflow (Wrap or Wraparound)" in the Common Weakness Enumeration catalog. The operational impact is particularly severe because the affected driver operates with elevated privileges in the backend context, meaning that any successful exploitation can result in complete system compromise.
The exploitation potential of this vulnerability extends beyond simple denial of service to encompass full privilege escalation capabilities and information disclosure attacks. Attackers can leverage this flaw to perform out-of-bounds memory reads and writes, potentially accessing sensitive kernel memory regions that contain credentials, encryption keys, or other confidential data. The attack surface is particularly concerning in virtualized environments where frontend components typically run with reduced privileges but can influence backend operations through the Xen hypervisor interface. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1068 as "Exploitation for Privilege Escalation" and T1499 as "Endpoint Denial of Service" in the MITRE ATT&CK framework. The vulnerability can be exploited by malicious frontends within the same virtual machine or by compromised frontend components that have gained access to the virtualization layer, making it a significant concern for cloud providers and organizations relying on Xen-based virtualization infrastructure.
Mitigation strategies for CVE-2018-15471 require immediate kernel updates and patches to address the integer overflow conditions in the hash mapping implementation. Organizations should prioritize patching affected Linux kernel versions to 4.18.2 or later, which contain the necessary fixes for the validation logic in the xenvif_set_hash_mapping function. Additionally, implementing network segmentation and access controls to limit frontend privileges within virtualized environments can reduce the attack surface. System administrators should also consider disabling unnecessary Xen features and implementing monitoring for suspicious hash mapping operations. The fix typically involves adding proper input validation checks and bounds verification before any memory allocation or access operations, ensuring that integer values used in hash calculations remain within safe operational limits. Organizations running Xen hypervisor versions through 4.11.x should upgrade to patched versions immediately, as the vulnerability affects the core virtualization infrastructure and can be exploited without requiring local access to the target system.