CVE-2025-38087: Linux Kernel Use-After-Free Vulnerability

CVE-2025-38087 Overview

CVE-2025-38087 is a use-after-free vulnerability in the Linux kernel's net/sched subsystem, specifically in the taprio_dev_notifier() function of the Time-Aware Priority Scheduler (taprio) queueing discipline. The function operates without an RCU (Read-Copy-Update) read-side critical section, creating a race condition with advance_sched() that can result in access to freed memory. The vulnerability is classified as [CWE-416] Use After Free and affects local attackers with low privileges on systems using the taprio qdisc. Successful exploitation can lead to kernel memory corruption, privilege escalation, or system compromise.

Critical Impact
A local attacker with low privileges can trigger a race condition in the taprio scheduler to achieve use-after-free memory access, potentially leading to kernel privilege escalation or denial of service.

Affected Products

Linux Kernel (multiple stable branches prior to the fix commits)
Linux Kernel 6.16-rc1
Linux Kernel 6.16-rc2

Discovery Timeline

2025-06-30 - CVE-2025-38087 published to NVD
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2025-38087

Vulnerability Analysis

The vulnerability resides in the taprio (Time-Aware Priority Scheduler) queueing discipline within the Linux kernel network scheduler. The taprio_dev_notifier() function handles network device notification events but fails to hold an RCU read-side lock while accessing RCU-protected data structures. Meanwhile, the advance_sched() function can concurrently update the scheduler state and free previously referenced objects. This creates a classic race window where taprio_dev_notifier() dereferences a pointer to memory that advance_sched() has already released. The result is a kernel-space use-after-free condition affecting memory integrity.

Root Cause

The root cause is missing RCU synchronization in taprio_dev_notifier(). RCU protects readers from observing intermediate states during updates, but only when readers explicitly enter a read-side critical section via rcu_read_lock(). Without this protection, the taprio notifier can hold stale references to scheduler objects that advance_sched() reclaims. The fix adds rcu_read_lock() and the corresponding rcu_read_unlock() around the affected pointer accesses in taprio_dev_notifier().

Attack Vector

Exploitation requires local access to the target system and the ability to configure or trigger taprio qdisc operations, typically requiring CAP_NET_ADMIN in a namespace or interaction with a device using taprio. An attacker races network device notifier events against active taprio scheduling to force the kernel to dereference freed memory. Depending on memory layout and heap grooming, this can be leveraged for information disclosure, denial of service through kernel panic, or arbitrary code execution in kernel context leading to privilege escalation.

No public proof-of-concept exploit has been published for this issue. Refer to the upstream fix commits listed in the Linux Kernel Commit b160766 and related patches for technical details.

Detection Methods for CVE-2025-38087

Indicators of Compromise

Unexpected kernel oops or panic messages referencing taprio_dev_notifier, advance_sched, or net/sched/sch_taprio.c in dmesg or journalctl -k output.
KASAN (Kernel Address Sanitizer) reports flagging use-after-free events in the taprio code path on kernels compiled with debugging enabled.
Anomalous privilege escalation events on hosts running taprio qdisc configurations, particularly on multi-tenant Linux systems.

Detection Strategies

Inventory Linux hosts and identify systems running taprio qdisc using tc qdisc show and correlate with the affected kernel versions.
Monitor kernel logs for repeated crashes or scheduler warnings tied to network device state transitions.
Deploy runtime kernel exploit detection tools capable of identifying suspicious kernel memory access patterns and unexpected privilege transitions.

Monitoring Recommendations

Enable auditd rules to log tc and netlink operations that create or modify taprio qdiscs.
Alert on kernel-space process behavior anomalies, such as unprivileged users gaining root capabilities after network subsystem activity.
Aggregate kernel crash telemetry centrally to correlate potential exploitation attempts across the fleet.

How to Mitigate CVE-2025-38087

Immediate Actions Required

Apply the upstream kernel patches referenced in the vendor advisories to all affected Linux systems, prioritizing multi-tenant, container host, and network-facing workloads.
Restrict CAP_NET_ADMIN and unprivileged user namespace creation on systems that do not require it to reduce the attack surface for qdisc manipulation.
Audit systems for taprio qdisc usage and disable it where it is not operationally required.

Patch Information

The Linux kernel maintainers resolved the issue by adding rcu_read_lock() inside taprio_dev_notifier() to establish a proper RCU read-side critical section. Fix commits are available at Linux Kernel Commit 8a008c8, Linux Kernel Commit 8c5713c, Linux Kernel Commit b1547d2, and Linux Kernel Commit b160766. Consume the fix through your distribution's stable kernel updates.

Workarounds

Remove or avoid configuring the taprio qdisc on affected hosts until patched kernels are deployed.
Constrain network configuration privileges by disabling kernel.unprivileged_userns_clone where feasible, blocking unprivileged access to qdisc manipulation.
Enable kernel hardening features such as KASLR, SMEP, SMAP, and CONFIG_SLAB_FREELIST_HARDENED to increase the difficulty of use-after-free exploitation.

bash

# Check for taprio qdisc usage across interfaces
tc qdisc show | grep -i taprio

# Restrict unprivileged user namespaces (reduces attack surface)
sysctl -w kernel.unprivileged_userns_clone=0

# Verify running kernel version and update via distribution package manager
uname -r
# Example for Debian/Ubuntu:
# sudo apt update && sudo apt upgrade linux-image-$(uname -r | cut -d- -f2-)