CVE-2024-36909 in Linux
Summary
by MITRE • 05/30/2024
In the Linux kernel, the following vulnerability has been resolved:
Drivers: hv: vmbus: Don't free ring buffers that couldn't be re-encrypted
In CoCo VMs it is possible for the untrusted host to cause set_memory_encrypted() or set_memory_decrypted() to fail such that an error is returned and the resulting memory is shared. Callers need to take care to handle these errors to avoid returning decrypted (shared) memory to the page allocator, which could lead to functional or security issues.
The VMBus ring buffer code could free decrypted/shared pages if set_memory_decrypted() fails. Check the decrypted field in the struct vmbus_gpadl for the ring buffers to decide whether to free the memory.
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Analysis
by VulDB Data Team • 09/30/2025
The vulnerability identified as CVE-2024-36909 resides within the Linux kernel's Hyper-V VMBus driver implementation, specifically affecting the handling of memory encryption states during ring buffer operations. This issue manifests in Confidential Computing (CoCo) virtual machines where the untrusted host component can manipulate memory encryption status through the set_memory_encrypted() and set_memory_decrypted() kernel functions. When these memory management functions encounter failures, they return error codes indicating that the memory operation could not be completed successfully, resulting in memory that remains in a shared state rather than achieving the desired encrypted or decrypted condition. The root cause stems from inadequate error handling within the VMBus ring buffer management code, which fails to properly account for the encryption state of memory pages when determining whether to release allocated resources back to the system's memory allocator. This flaw represents a critical security concern as it can lead to memory corruption or information disclosure when decrypted or shared memory pages are inadvertently returned to the page allocator for reuse.
The technical implementation of this vulnerability involves the vmbus_gpadl structure which manages guest physical address descriptor lists for VMBus communication channels. When set_memory_decrypted() fails during ring buffer cleanup operations, the code path does not properly verify the decrypted field within the vmbus_gpadl structure before proceeding with memory deallocation. This oversight creates a scenario where memory pages that were not successfully decrypted remain in a shared state and could be accessed by unauthorized entities or corrupted through improper memory reuse. The vulnerability specifically affects the memory management subsystem's ability to maintain proper encryption boundaries, potentially allowing malicious host components to exploit the inconsistent memory state for privilege escalation or data leakage attacks. The flaw demonstrates poor adherence to secure memory management practices where error conditions are not adequately handled to maintain system integrity.
The operational impact of CVE-2024-36909 extends beyond simple memory management issues to encompass potential security breaches in confidential computing environments where data protection is paramount. In CoCo VMs, this vulnerability could enable attackers to gain access to sensitive information that should remain encrypted, as the system fails to properly handle memory states when decryption operations fail. The vulnerability is particularly concerning for cloud environments where multiple tenants share the same physical infrastructure, as it could allow one tenant to potentially access or corrupt another tenant's encrypted memory space. System administrators may observe unexpected memory allocation patterns or potential stability issues when this vulnerability is exploited, though the primary risk lies in the potential for information disclosure rather than direct system compromise. This issue directly relates to CWE-119 which addresses improper access to memory locations and CWE-310 which covers cryptographic issues in memory management.
Mitigation strategies for CVE-2024-36909 require immediate kernel updates to address the memory handling logic in the VMBus driver component. System administrators should prioritize patching affected systems, particularly those running in confidential computing environments or cloud deployments where CoCo VMs are utilized. The fix implemented in the kernel involves adding proper error checking for the decrypted field in vmbus_gpadl structures before memory deallocation occurs, ensuring that only properly decrypted pages are freed back to the allocator. Organizations should also implement monitoring for unusual memory allocation patterns or potential attempts to exploit memory management vulnerabilities. Security teams should review their confidential computing configurations and verify that memory encryption states are properly maintained throughout the system lifecycle. This vulnerability aligns with ATT&CK technique T1059 which covers command and scripting interpreter usage, and T1566 which addresses credential access through system compromise, as it creates opportunities for attackers to manipulate memory states and potentially gain unauthorized access to protected information. The fix demonstrates the importance of robust error handling in kernel memory management functions and proper state verification before resource deallocation operations.