Linux Kernel up to 6.18.38/7.1.3 KVM handle_tpr_below_threshold denial of service

CVSS Meta Temp Score
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CTI Interest Score
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6.2$0-$5k3.88-

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.18.38/7.1.3 and classified as critical. Affected by this issue is the function handle_tpr_below_threshold of the component KVM. Executing a manipulation can lead to denial of service. This vulnerability is handled as CVE-2026-64513. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.18.38/7.1.3 and classified as critical. This vulnerability affects the function handle_tpr_below_threshold of the component KVM. The manipulation with an unknown input leads to a denial of service vulnerability. The CWE definition for the vulnerability is CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. As an impact it is known to affect availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Unconditionally recompute CR8 intercept on PPR update The TPR_THRESHOLD field in the VMCS is used by VMX to induce VM exits when the guest's virtual TPR falls under the specified threshold, allowing KVM to inject previously masked interrupts. KVM handles these VM exits in handle_tpr_below_threshold(). Commit eb90f3417a0c ("KVM: vmx: speed up TPR below threshold vmexits") optimized this function by calling apic_update_ppr() instead of raising KVM_REQ_EVENT. apic_update_ppr() then raises KVM_REQ_EVENT if there is a pending, deliverable interrupt. However, if there are no new interrupts pending, apic_update_ppr() does not issue the request. Thus, kvm_lapic_update_cr8_intercept() and vmx_update_cr8_intercept() are not called before VM entry, which results in a high, stale TPR_THRESHOLD. This is problematic due to the following sentence in 28.2.1.1 "VM-Execution Control Fields" in the SDM: The following check is performed if the “use TPR shadow” VM-execution control is 1 and the “virtualize APIC accesses” and “virtual-interrupt delivery” VM-execution controls are both 0: the value of bits 3:0 of the TPR threshold VM-execution control field should not be greater than the value of bits 7:4 of VTPR. This error condition is typically not observed when KVM runs on a bare metal system because modern processors support APICv, which enables virtual-interrupt delivery, and which KVM uses when possible. This causes the processor to no longer generate TPR-below-threshold exits and to no longer check TPR_THRESHOLD on entry. However, when running on older platforms, or under nested virtualization on a hypervisor that does not support virtual-interrupt delivery and enforces this check (like Hyper-V) this can cause a VM entry failure with hardware error 0x7, as seen in [1]. Call kvm_lapic_update_cr8_intercept() if apic_update_ppr() does not find a deliverable interrupt (and thus does not raise KVM_REQ_EVENT). Remove calls to kvm_lapic_update_cr8_intercept() on paths that end up in apic_update_ppr(), as they now become redundant. This ensures that any path that updates the guest's PPR also figures out if KVM needs to wait for a TPR change (using TPR_THRESHOLD on VMX or CR8 intercepts on SVM).

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-64513 since 07/19/2026. The exploitation appears to be easy. The attack can be initiated remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 07/26/2026). The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 6.18.39, 7.1.4 or 7.2-rc1 eliminates this vulnerability. Applying the patch ff9c4c6428883182960cfe5c78928f0896d80ebc/8c8e8ac22ee17d52f9eb2bc814bca7fab90fb8df/bb365a506b1e6fb050c0fceaad354fe395385ef0 is able to eliminate this problem.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-48857). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.5
VulDB Meta Temp Score: 6.2

VulDB Base Score: 6.5
VulDB Temp Score: 6.2
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Denial of service
CWE: CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.18.39/7.1.4/7.2-rc1
Patch: ff9c4c6428883182960cfe5c78928f0896d80ebc/8c8e8ac22ee17d52f9eb2bc814bca7fab90fb8df/bb365a506b1e6fb050c0fceaad354fe395385ef0

Timelineinfo

07/19/2026 CVE reserved
07/25/2026 +6 days Advisory disclosed
07/25/2026 +0 days VulDB entry created
07/26/2026 +1 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-64513 (🔒)
GCVE (CVE): GCVE-0-2026-64513
GCVE (VulDB): GCVE-100-383296
EUVD: 🔒

Entryinfo

Created: 07/25/2026 19:19
Updated: 07/26/2026 02:04
Changes: 07/25/2026 19:19 (58), 07/26/2026 02:04 (1)
Complete: 🔍
Cache ID: 216::103

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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