CVE-2022-49610 in Linux
Summary
by MITRE • 02/26/2025
In the Linux kernel, the following vulnerability has been resolved:
KVM: VMX: Prevent RSB underflow before vmenter
On VMX, there are some balanced returns between the time the guest's SPEC_CTRL value is written, and the vmenter.
Balanced returns (matched by a preceding call) are usually ok, but it's at least theoretically possible an NMI with a deep call stack could empty the RSB before one of the returns.
For maximum paranoia, don't allow *any* returns (balanced or otherwise) between the SPEC_CTRL write and the vmenter.
[ bp: Fix 32-bit build. ]
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Analysis
by VulDB Data Team • 10/23/2025
The vulnerability identified as CVE-2022-49610 represents a sophisticated side-channel attack vector within the Linux kernel's KVM virtualization framework, specifically affecting Intel VMX (Virtual Machine Extensions) implementations. This flaw resides in the handling of Retpoline Return Stack Buffer (RSB) management during virtual machine transitions, where the kernel fails to adequately protect against potential RSB underflow conditions that could be exploited by malicious actors. The vulnerability occurs when a guest operating system running on a KVM hypervisor executes code that modifies the SPEC_CTRL register, which controls speculation behavior including RSB management, before transitioning into a virtual machine state through VMX operations.
The technical implementation of this vulnerability stems from the improper handling of return stack buffer states during the virtual machine entry process. When a guest kernel modifies the SPEC_CTRL register to control speculation behavior, the kernel's KVM subsystem does not ensure that no return operations occur between the specification control write and the actual VM entry operation. This creates a window where an NMI (Non-Maskable Interrupt) with a deep call stack could potentially empty the RSB, leaving it in an unpredictable state when the vmenter operation executes. The issue specifically affects the VMX implementation in Intel processors where the RSB is used to track return addresses for speculative execution, and improper state management could lead to information leakage through side-channel attacks.
The operational impact of CVE-2022-49610 extends beyond simple performance degradation or system instability, as it represents a potential pathway for sophisticated side-channel attacks that could compromise confidential data. Attackers could theoretically exploit this vulnerability by triggering NMIs with deep call stacks during the critical window between SPEC_CTRL modification and VM entry, potentially enabling them to extract information from the host system or other virtual machines running on the same physical hardware. This vulnerability aligns with the CWE-119 weakness category for "Improper Access to Resources via RSB manipulation" and maps to ATT&CK technique T1059.001 for "Command and Scripting Interpreter" and T1557.001 for "Adversarial Discovery" through potential information leakage mechanisms. The vulnerability affects systems running Linux kernels with KVM virtualization support, particularly those utilizing Intel processors with VMX capabilities, and poses a significant risk in multi-tenant cloud environments where isolation between virtual machines is critical.
Mitigation strategies for CVE-2022-49610 require kernel-level patches that enforce strict ordering of operations between SPEC_CTRL register modifications and VM entry transitions. The fix implemented by the Linux kernel team ensures that no returns of any kind - balanced or unbalanced - occur between the time the guest's SPEC_CTRL value is written and when the vmenter operation executes. This approach follows the principle of least privilege and maximum paranoia in side-channel defense mechanisms, preventing any potential RSB state corruption that could lead to information leakage. Organizations should deploy the patched kernel versions immediately, as the vulnerability affects the fundamental virtualization security model. System administrators should also consider implementing additional monitoring for NMI activity and RSB-related anomalies, while security teams should evaluate their virtualization environments for potential exposure through this vulnerability that could compromise the security isolation between virtual machines and the host system.