high · CVSS v3 7.1

CVE-2026-98625

A use‑after‑free occurs in the Linux kernel netfilter flowtable when a flow is marked HW_DEAD before clearing HW_PENDING, allowing RCU to fr

Overview

A use‑after‑free occurs in the Linux kernel netfilter flowtable when a flow is marked HW_DEAD before clearing HW_PENDING, allowing RCU to free the object while a worker still accesses it. This flaw can lead to memory corruption or crashes in systems that use flow offloading. It affects all Linux kernel versions prior to the patch that moves HW_DEAD publication to the worker epilogue.

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: flowtable: publish HW_DEAD after worker is done flow_offload_work_del() sets NF_FLOW_HW_DEAD before the work handler clears NF_FLOW_HW_PENDING. Once a flow is both HW_DYING and HW_DEAD, a concurrent garbage collection pass can remove it and schedule it for RCU freeing. The offload worker holds neither an RCU read lock nor a reference to the flow. If it is preempted after publishing HW_DEAD, the RCU callback can free the flow before the worker resumes and clears HW_PENDING, resulting in a use-after-free. Move HW_DEAD publication to the common worker epilogue after the pending bit is cleared, making it the final flow access by destroy work. Order all preceding flow accesses before publishing the bit that allows garbage collection to free the object.

Impact

The vulnerability compromises confidentiality, integrity, and availability by enabling memory corruption that could be leveraged to crash the kernel or execute arbitrary code. System administrators and security teams are impacted as the flaw resides in core networking components.

Remediation

Upgrade to a kernel version that includes the CVE‑2026‑98625 fix or apply the upstream patch. If upgrading is not immediately possible, disable netfilter flow offloading or set CONFIG_NETFILTER_XT_MATCH_FLOWTABLE to off. Ensure RCU and memory protection options (e.g., CONFIG_RCU_NOCB_CPU) are enabled.

Risk context

Severity is high with a CVSS v3 score of 7.1. No EPSS data is available, but the flaw can cause kernel crashes, warranting prompt patching.

Affected products

  • Linux kernel

Scores

Severity
high
CVSS v2
5.6
CVSS v3
7.1
CVSS v4
—
EPSS
—

kernel netfilter use-after-free rcu memory-corruption high-severity patch

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