CVE-2026-98551
Received Received - Intake

Uninitialized Memory Disclosure in Linux Kernel perf/core

Publication date: 2026-10-18

Last updated on: 2026-10-18

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: perf/core: Fill branch entries with a single assignment perf_clear_branch_entry_bitfields() clears the bitfields of struct perf_branch_entry one by one and leaves from/to alone, since callers overwrite those straight away. The list has to be kept in sync with the struct by hand and has already fallen behind: new_type and priv were added to perf_branch_entry and never added here. Only BRBE writes those two, and neither for every record. brbe_set_perf_entry_type() leaves new_type alone for a branch type it does not recognise, and priv is not set for source-only records. arm_pmuv3.c allocates the per-CPU branch stack with kmalloc(), so such a record reaches userspace with whatever the slot held: uninitialised kmalloc() data on the first pass over the buffer, the previous record's values after that. Nothing under arch/x86/events/ writes either field, so only arm64 is affected. Assign the whole entry at each site instead. Everything not named is then zero, and there is no list to keep in sync. The bitfields add up to exactly 64 bits, so the struct has no padding to leave undefined. perf_clear_branch_entry_bitfields() has no callers left, so remove it. perf_entry_from_brbe_regset() assigns an empty literal instead, since it fills from/to conditionally. PERF_BR_SPEC_NA is 0, so dropping the explicit spec assignment changes nothing.

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Meta Information

Published
2026-10-18
Last Modified
2026-10-18
Generated
2026-10-18
AI Q&A
2026-10-18
EPSS Evaluated
N/A
NVD
CVE-2026-98551
EUVD
EUVD-2026-103596

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
Linux Linux b190bc4ac9e6d9763b61654c5a0c085ff77d7a09
Linux Linux b190bc4ac9e6d9763b61654c5a0c085ff77d7a09
Linux Linux 6.1

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a Linux kernel vulnerability where the perf subsystem incorrectly clears and manages branch entry data structures. The issue stems from manually clearing bitfields in perf_branch_entry while leaving other fields uninitialized, leading to potential exposure of sensitive memory contents like uninitialized kmalloc data or previous record values.

Detection Guidance

This vulnerability is specific to the Linux kernel's perf subsystem on arm64 systems. Detection requires checking kernel version and perf subsystem behavior. No direct commands are provided in the context, but monitoring for unexpected perf branch entry values or crashes in perf-related tools may indicate exploitation.

Impact Analysis

On affected arm64 systems, this flaw could allow local attackers to read sensitive kernel memory contents. The vulnerability exposes data from previous operations or uninitialized memory, potentially leaking passwords, encryption keys, or other confidential information.

Mitigation Strategies

Update the Linux kernel to the latest patched version. Since this is a kernel-level issue, applying vendor security updates is the primary mitigation. No additional steps are specified in the context.

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