CVE-2026-98049

Modified Modified - Updated After Analysis

BPF Arena 32-bit Cmpxchg Zero Extension Issue

Publication date: 2026-09-25

Last updated on: 2026-10-15

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: zero extend the result of an arena 32-bit cmpxchg bpf_convert_ctx_accesses() rewrites an atomic on an arena pointer from BPF_STX | BPF_ATOMIC to BPF_STX | BPF_PROBE_ATOMIC, and it runs before bpf_opt_subreg_zext_lo32_rnd_hi32(). That pass emits an explicit zero extension for a 32-bit cmpxchg even when bpf_jit_needs_zext() is false. This is done because on some architectures 32-bit cmpxchg requires explicit zero extension for the dst register. E.g. on x86-64 'lock cmpxchg' does not change the %eax if comparison is successful, while BPF semantics declare that each operation on a 32-bit register zero extends it's upper half. is_cmpxchg_insn() matches BPF_MODE == BPF_ATOMIC only, so an arena cmpxchg misses said zero extension adjustment. This patch adjusts is_cmpxchg_insn() to match BPF_PROBE_ATOMIC alongside BPF_ATOMIC.

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Meta Information

Published

2026-09-25

Last Modified

2026-10-15

Generated

2026-10-16

AI Q&A

2026-09-25

EPSS Evaluated

2026-10-14

NVD

CVE-2026-98049

EUVD

EUVD-2026-86702

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	7.3
linux	linux_kernel	From 6.10 (inc) to 7.2.7 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-681	When converting from one data type to another, such as long to integer, data can be omitted or translated in a way that produces unexpected values. If the resulting values are used in a sensitive context, then dangerous behaviors may occur.

Attack-Flow Graph

Executive Summary

This is a Linux kernel vulnerability where a 32-bit cmpxchg operation on an arena pointer is not properly zero-extended. The bpf_convert_ctx_accesses() function rewrites atomic operations but runs before the zero-extension pass. This causes issues on some architectures where 32-bit cmpxchg requires explicit zero extension for the destination register.

Detection Guidance

This vulnerability is specific to the Linux kernel's BPF (Berkeley Packet Filter) implementation and requires kernel-level inspection. Detection involves checking kernel version and BPF-related components. Use 'uname -r' to check kernel version and 'lsmod | grep bpf' to verify BPF module status. No direct network detection commands are applicable as this is a local kernel issue.

Impact Analysis

This vulnerability could lead to incorrect behavior in BPF programs using arena pointers with 32-bit cmpxchg operations. It may cause data corruption or unexpected system behavior if the upper bits of registers are not properly zeroed after cmpxchg operations.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards. It is a low-level Linux kernel issue related to BPF atomic operations and zero-extension handling, which does not introduce data breaches or unauthorized access risks that would impact regulatory compliance.

Mitigation Strategies

Update the Linux kernel to the latest patched version to resolve this vulnerability. Monitor vendor advisories for kernel updates and apply them promptly.

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