External risk intelligence

Linux Kernel Ceph Use-After-Free Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2023-53867

This vulnerability exists within the Linux kernel's Ceph file system client code. Kernel-level vulnerabilities in specific file system drivers are typically not exposed directly to the internet; they require local access or specific, already-compromised conditions to trigger and are not standard public-facing network services.

Use After Free

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This critical vulnerability in the Linux kernel's Ceph file system client could allow for system crashes. While the core issue is a technical memory management problem, its potential impact necessitates confirming its relevance within our environment.

A rare kernel bug could cause system instability.
Leadership should note potential impact on specific storage systems.
Confirm relevance and exposure in our storage infrastructure.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by interacting with the Ceph file system in a way that causes a race condition between threads. This race condition could lead to a use-after-free error when memory is accessed after it has been deallocated, potentially crashing the system.

No special access needed.
Trimming caps triggers memory issue.
System crash may occur.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in the Linux kernel's Ceph client could potentially lead to a denial-of-service condition. When specific operations related to session capabilities occur concurrently, a race condition might cause the system to crash. This crash could impact the availability of services that rely on the affected kernel component.

System stability could be affected.
Concurrent operations may trigger a crash.
Service availability could be impacted.

Operational Fix

Recommended remediation, mitigation, and detection steps

The Linux kernel's Ceph file system component is affected by this use-after-free vulnerability. Ownership likely resides with the infrastructure or platform team managing the Ceph storage environment, with coordination potentially needed from the vendor-management team if Ceph was procured as a managed service. The immediate first step is to identify all systems running the affected Ceph kernel components, assess their exposure and criticality, and then confirm the accountable owner for remediation.

Infrastructure/platform team owns remediation.
Verify Ceph deployments and exposure.
Plan maintenance for fix deployment.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the Linux kernel Ceph file system client?

The Ceph file system client is a component within the Linux kernel that allows a computer to mount and interact with Ceph storage clusters. It manages how the operating system reads, writes, and handles metadata for these distributed, highly scalable storage environments, acting as a translator between your local applications and the remote Ceph storage.

Why is CVE-2023-53867 called a use-after-free bug?

This vulnerability is a memory management error where the kernel continues to reference a piece of memory after it has been deleted or freed. In this specific case, a race condition occurs during the process of trimming session capabilities, leading the system to attempt to use stale memory, which causes a crash.

How can an attacker trigger this kernel memory issue?

The flaw is triggered by specific, concurrent interactions with the Ceph file system, specifically during the cap-trimming process. It requires a precise race condition between two separate threads. Simply reading or writing files normally does not necessarily trigger this; the crash relies on a specific timing gap where one thread removes a capability just as another thread attempts to use it.

Is this CVE a risk for my internet-facing services?

According to Halo Surface Signal, this vulnerability is very unlikely to be exposed to the internet. Because it resides deep within the Linux kernel's Ceph driver, it generally requires local access or a highly specific, already-compromised environment to reach and manipulate, rather than being reachable through standard public-facing network services.

Do I need to take immediate action to fix this?

Start by identifying all infrastructure using the Ceph file system client. Coordinate with your platform or storage teams to confirm which systems are running the affected kernel versions. Once you have an inventory, assess the criticality of those storage systems and plan a standard maintenance cycle to apply the necessary kernel updates.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.