CVE-2026-89928 : 상세 정보

CVE-2026-89928

8.8
/
높음
2026-09-16
11h17 +00:00
Local
2026-10-19
09h18 +00:00
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CVE 설명

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Consume the locked rmap value in the lockless rmap walk __kvm_rmap_lock() deliberately elides the rmap lock when it observes an empty rmap. In that case kvm_rmap_lock_readonly() also re-enables preemption and returns zero, so the caller holds neither the rmap lock nor a preemption reference. The elision documents the invariant it relies on: * Elide the lock if the rmap is empty, as lockless walkers (read-only * mode) don't need to (and can't) walk an empty rmap, nor can they add * entries to the rmap. I.e. the only paths that process empty rmaps * do so while holding mmu_lock for write, and are mutually exclusive. kvm_rmap_age_gfn_range() ignores the returned value and unconditionally enters for_each_rmap_spte_lockless(). The iterator started with rmap_get_first(), which re-reads rmap_head->val rather than using the value returned by the lock. If a writer populates the rmap between the lock's read and the iterator's re-read, the aging path walks the newly installed rmap without holding its lock. For a KVM_RMAP_MANY rmap this leaves the walker following a pte_list_desc chain that it never locked. A writer holding mmu_lock for write may free that chain (e.g. kvm_zap_all_rmap_sptes() on the recycle path, or any rmap zap) via kmem_cache_free() while the walk is in progress, giving a slab use-after-free. Nothing serialises the two: the aging path runs without mmu_lock when CONFIG_KVM_MMU_LOCKLESS_AGING=y, and the rmap lock that would otherwise exclude the writer was elided. Because the empty path re-enables preemption, the interval between the two reads can span an arbitrary scheduling delay. Fix the class of bug by having the lockless walk consume the value returned by the lock instead of re-reading the rmap. Split rmap_get_first() into __rmap_get_first(), which starts an iterator from an already-read rmap value, and make for_each_rmap_spte_lockless() take that value and call __rmap_get_first() directly. kvm_rmap_age_gfn_range() passes the value returned by kvm_rmap_lock_readonly(): when the lock was elided the value is zero, __rmap_get_first() returns NULL, and the walk is skipped. No lockless walker re-reads the rmap, so the lock-elision invariant cannot be violated, and no lock()-without-paired-unlock() path is added to the aging code.

CVE 정보

메트릭

메트릭 점수 심각도 CVSS 벡터 출처
V3.1 8.8 HIGH CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Base: Exploitabilty Metrics

The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component.

Attack Vector

This metric reflects the context by which vulnerability exploitation is possible.

Local

The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities.

Attack Complexity

This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability.

Low

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.

Privileges Required

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

Low

The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.

User Interaction

This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope.

Scope

Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs.

Changed

An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.

Base: Impact Metrics

The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve.

Confidentiality Impact

This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability.

High

There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.

Integrity Impact

This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information.

High

There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.

Availability Impact

This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability.

High

There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Temporal Metrics

The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability.

Environmental Metrics

These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.

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