CVE-2026-98937 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
perf/core: Check kernel access when kernel callchains are requested
perf_event_open() currently gates perf_allow_kernel() only on !attr.exclude_kernel.
However, users can still request kernel callchain collection with attr.exclude_callchain_kernel == 0 even when attr.exclude_kernel == 1. That still requires kernel profiling privilege, but the existing check does not enforce it.
Update the permission check to call perf_allow_kernel() when either kernel sampling is requested or kernel callchains are requested.
This keeps permission checks aligned with requested data and prevents unprivileged use of kernel callchain capture.
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Analysis
by VulDB Data Team • 10/23/2026
The Linux kernel's performance monitoring subsystem, specifically within the perf/core module, contained a logic flaw in its access control mechanisms for capturing kernel-level execution traces. The vulnerability arises from an inconsistency between how different types of kernel profiling data are gated by permission checks during the initialization of performance events via the perf_event_open system call. Historically, the code enforced strict privilege requirements only when general kernel sampling was explicitly requested through the attr.exclude_kernel attribute being set to zero. This check relied on the perf_allow_kernel function to ensure that only processes with appropriate capabilities could access sensitive kernel data. However, this security boundary failed to account for a specific configuration path where users could request the collection of kernel callchains independently of general kernel sampling.
The technical flaw manifests when an unprivileged user sets attr.exclude_callchain_kernel to zero while simultaneously setting attr.exclude_kernel to one. In this scenario, the application indicates it does not want general kernel samples but explicitly requests that if any profiling data is collected, it should include detailed stack traces originating from kernel space. The existing code logic did not trigger the perf_allow_kernel check in this specific configuration because the primary gate was tied solely to the exclude_kernel flag. Consequently, an attacker or a malicious application running with standard user privileges could bypass the intended security restrictions and capture sensitive information about kernel execution paths, including function addresses, return pointers, and potentially internal state details that are not exposed through normal interfaces.
This misconfiguration represents a classic access control bypass where the granularity of permission checks does not align with all vectors of data exfiltration. By allowing unprivileged processes to request kernel callchains without verifying their privileges, the system exposes itself to information disclosure risks. The captured callchain data can be used for reconnaissance purposes, helping attackers map out kernel modules, identify loaded security patches or mitigations, and understand the internal structure of the operating system to craft more effective exploits against specific versions of Linux. This aligns with CWE-269 Improper Privilege Management, as the software fails to enforce required privileges when accessing resources that require higher levels of trust. Furthermore, this behavior facilitates unauthorized data collection which can be categorized under ATT&CK technique T1057 Process Discovery or more specifically information gathering related to system architecture analysis in a Linux environment.
The operational impact of this vulnerability is primarily centered on the potential for privilege escalation through enhanced reconnaissance and the violation of isolation boundaries between user space and kernel space. While capturing callchains does not directly allow code execution, it provides critical intelligence that lowers the barrier for subsequent attacks. In high-security environments where strict separation of duties is enforced, such as in multi-tenant cloud infrastructure or hardened server deployments, this flaw undermines the security model by allowing lower-privileged tenants to inspect kernel behavior of other processes or system services running on the same host. This can lead to a degradation of overall system integrity and confidentiality.
To mitigate this vulnerability, the Linux kernel developers have updated the permission logic within perf_event_open to ensure that perf_allow_kernel is invoked whenever either general kernel sampling is requested via attr.exclude_kernel being zero OR when kernel callchain collection is explicitly enabled by setting attr.exclude_callchain_kernel to zero. This change ensures that any request for sensitive kernel-side data, regardless of whether it involves raw samples or just stack traces, triggers the appropriate privilege verification. Administrators and users should ensure they are running a patched version of the Linux kernel where this logic has been corrected. Additionally, organizations relying on perf tools for monitoring should audit their configurations to ensure that callchain collection is disabled unless absolutely necessary for debugging by privileged personnel, thereby reducing the attack surface even if patching is delayed.