CVE-2025-38684
Medium · 5.5CVSS
5.5
EPSS
0.2%
Published
Sep 4, 2025
CISA due date
—
Cloudanix analysis
A bug in the Linux kernel's network traffic scheduler lets a local user crash the entire system by changing certain configuration settings.
- Exploitation
- Local Privilege
- Attacker needs
- Low Privilege
- Complexity
- Low
- Impact
- Denial Of Service
- Component
- OS kernel
- Class
- Memory Corruption
- Remediation
- Upgrade
- Effort
- Medium
- Patch risk
- Low
What it actually does
The flaw triggers a NULL pointer dereference in __list_del_entry_valid_or_report called from ets_class_qlen_notify during ets_qdisc_change, because the purge of idle DWRR queues uses the newly assigned q->nbands and q->nstrict values instead of the previous ones, leaving ets_class_find and ets_class_is_strict operating on an inconsistent configuration.
Why it matters to the business
Local users on Linux systems using the ETS qdisc can crash the kernel, causing denial of service that disrupts network traffic shaping and requires a reboot; the issue affects many distributions and container environments where qdisc configuration changes occur.
How an attack unfolds
An authenticated local attacker invokes the netlink interface (via tc or direct sendmsg) to modify an ETS qdisc, forcing ets_qdisc_change to purge classes with the updated band count; this reaches ets_class_qlen_notify with a null list entry and dereferences a null pointer, producing the oops.
How to fix it
Update the Linux kernel to a version containing the fix that performs the DWRR purge using the old nbands and nstrict values before storing the new configuration; apply the referenced upstream commit that restores consistent state during ets_qdisc_change.
How to confirm the fix worked
Confirm the patch by inspecting the ets_qdisc_change function for the order of old-band purge before assignment of q->nbands, or run the sch_ets test case that previously triggered the crash and verify it no longer produces a NULL dereference.
Typical attack path
- Obtain a local shell or container with CAP_NET_ADMIN
- Issue a netlink RTM_NEWQDISC or RTM_DELQDISC message targeting sch_ets
- Supply a change that reduces the number of bands, triggering the inconsistent purge logic
- Cause the kernel NULL dereference and system crash
How to detect it
Search kernel logs for Oops entries referencing __list_del_entry_valid_or_report, ets_class_qlen_notify, or sch_ets during tc or netlink activity; correlate with processes invoking sendmsg on NETLINK_ROUTE sockets.
What your security team should do
- Apply the kernel fix immediately on all systems that load the sch_ets module
- Restrict CAP_NET_ADMIN to trusted processes only until patches are deployed
- Monitor for kernel oops messages containing ets_class_qlen_notify or sch_ets
- Test qdisc reconfiguration workloads in staging before production rollout
The record
In the Linux kernel, the following vulnerability has been resolved: net/sched: ets: use old 'nbands' while purging unused classes Shuang reported sch_ets test-case [1] crashing in ets_class_qlen_notify() after recent changes from Lion [2]. The problem is: in ets_qdisc_change() we purge unused DWRR queues; the value of 'q->nbands' is the new one, and the cleanup should be done with the old one. The problem is here since my first attempts to fix ets_qdisc_change(), but it surfaced again after the recent qdisc len accounting fixes. Fix it purging idle DWRR queues before assigning a new value of 'q->nbands', so that all purge operations find a consistent configuration: - old 'q->nbands' because it's needed by ets_class_find() - old 'q->nstrict' because it's needed by ets_class_is_strict() BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 62 UID: 0 PID: 39457 Comm: tc Kdump: loaded Not tainted 6.12.0-116.el10.x86_64 #1 PREEMPT(voluntary) Hardware name: Dell Inc. PowerEdge R640/06DKY5, BIOS 2.12.2 07/09/2021 RIP: 0010:__list_del_entry_valid_or_report+0x4/0x80 Code: ff 4c 39 c7 0f 84 39 19 8e ff b8 01 00 00 00 c3 cc cc cc cc 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa <48> 8b 17 48 8b 4f 08 48 85 d2 0f 84 56 19 8e ff 48 85 c9 0f 84 ab RSP: 0018:ffffba186009f400 EFLAGS: 00010202 RAX: 00000000000000d6 RBX: 0000000000000000 RCX: 0000000000000004 RDX: ffff9f0fa29b69c0 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffffffc12c2400 R08: 0000000000000008 R09: 0000000000000004 R10: ffffffffffffffff R11: 0000000000000004 R12: 0000000000000000 R13: ffff9f0f8cfe0000 R14: 0000000000100005 R15: 0000000000000000 FS: 00007f2154f37480(0000) GS:ffff9f269c1c0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 00000001530be001 CR4: 00000000007726f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> ets_class_qlen_notify+0x65/0x90 [sch_ets] qdisc_tree_reduce_backlog+0x74/0x110 ets_qdisc_change+0x630/0xa40 [sch_ets] __tc_modify_qdisc.constprop.0+0x216/0x7f0 tc_modify_qdisc+0x7c/0x120 rtnetlink_rcv_msg+0x145/0x3f0 netlink_rcv_skb+0x53/0x100 netlink_unicast+0x245/0x390 netlink_sendmsg+0x21b/0x470 ____sys_sendmsg+0x39d/0x3d0 ___sys_sendmsg+0x9a/0xe0 __sys_sendmsg+0x7a/0xd0 do_syscall_64+0x7d/0x160 entry_SYSCALL_64_after_hwframe+0x76/0x7e RIP: 0033:0x7f2155114084 Code: 89 02 b8 ff ff ff ff eb bb 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 80 3d 25 f0 0c 00 00 74 13 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 48 83 ec 28 89 54 24 1c 48 89 RSP: 002b:00007fff1fd7a988 EFLAGS: 00000202 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 0000560ec063e5e0 RCX: 00007f2155114084 RDX: 0000000000000000 RSI: 00007fff1fd7a9f0 RDI: 0000000000000003 RBP: 00007fff1fd7aa60 R08: 0000000000000010 R09: 000000000000003f R10: 0000560ee9b3a010 R11: 0000000000000202 R12: 00007fff1fd7aae0 R13: 000000006891ccde R14: 0000560ec063e5e0 R15: 00007fff1fd7aad0 </TASK> [1] https://lore.kernel.org/netdev/e08c7f4a6882f260011909a868311c6e9b54f3e4.1639153474.git.dcaratti@redhat.com/ [2] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/
Affected packages
| Ecosystem | Package | Introduced | Fixed |
|---|---|---|---|
| Debian:11 | linux | 0 | No fix |
| Debian:12 | linux | 0 | No fix |
| Debian:13 | linux | 0 | 6.12.43-1 |
| Debian:14 | linux | 0 | 6.16.3-1 |
| Linux | Kernel | 5.6.0 | 5.10.241 |
| Mageia:9 | kernel | 0 | 6.6.105-1.mga9 |
| Mageia:9 | kernel-linus | 0 | 6.6.105-1.mga9 |
| Mageia:9 | kmod-virtualbox | 0 | 7.1.10-10.mga9 |
| Mageia:9 | kmod-xtables-addons | 0 | 3.24-86.mga9 |
| Mageia:9 | mageia-repos | 0 | 9-4.mga9 |
| Mageia:9 | meta-task | 0 | 9-4.mga9 |
| SUSE:Linux Enterprise High Availability Extension 15 SP4 | kernel-default | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Availability Extension 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | kernel-64kb | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | kernel-default | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | kernel-default-base | 0 | 5.14.21-150400.24.194.1.150400.24.98.3 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | kernel-docs | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | kernel-obs-build | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | kernel-source | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | kernel-syms | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | kernel-64kb | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | kernel-default | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | kernel-default-base | 0 | 5.14.21-150400.24.194.1.150400.24.98.3 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | kernel-docs | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | kernel-obs-build | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | kernel-source | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | kernel-syms | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Live Patching 15 SP4 | kernel-default | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Live Patching 15 SP4 | kernel-livepatch-SLE15-SP4_Update_48 | 0 | 1-150400.9.7.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-livepatch-SLE15-SP6-RT_Update_16 | 0 | 1-150600.1.3.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-livepatch-SLE15-SP6_Update_16 | 0 | 1-150600.13.3.1 |
| SUSE:Linux Enterprise Live Patching 15 SP7 | kernel-livepatch-SLE15-SP7-RT_Update_5 | 0 | 1-150700.1.3.1 |
| SUSE:Linux Enterprise Micro 5.3 | kernel-default | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Micro 5.3 | kernel-default-base | 0 | 5.14.21-150400.24.194.1.150400.24.98.3 |
| SUSE:Linux Enterprise Micro 5.4 | kernel-default | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Micro 5.4 | kernel-default-base | 0 | 5.14.21-150400.24.194.1.150400.24.98.3 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-64kb | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-default-base | 0 | 6.4.0-150600.23.73.1.150600.12.32.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-source | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-zfcpdump | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-docs | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-obs-build | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-source | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-syms | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Legacy 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-azure | 0 | 6.4.0-150600.8.52.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-source-azure | 0 | 6.4.0-150600.8.52.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-syms-azure | 0 | 6.4.0-150600.8.52.1 |
| SUSE:Linux Enterprise Server 15 SP4-LTSS | kernel-64kb | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server 15 SP4-LTSS | kernel-default | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server 15 SP4-LTSS | kernel-default-base | 0 | 5.14.21-150400.24.194.1.150400.24.98.3 |
| SUSE:Linux Enterprise Server 15 SP4-LTSS | kernel-docs | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server 15 SP4-LTSS | kernel-obs-build | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server 15 SP4-LTSS | kernel-source | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server 15 SP4-LTSS | kernel-syms | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server 15 SP4-LTSS | kernel-zfcpdump | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server for SAP Applications 15 SP4 | kernel-default | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server for SAP Applications 15 SP4 | kernel-default-base | 0 | 5.14.21-150400.24.194.1.150400.24.98.3 |
| SUSE:Linux Enterprise Server for SAP Applications 15 SP4 | kernel-docs | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server for SAP Applications 15 SP4 | kernel-obs-build | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server for SAP Applications 15 SP4 | kernel-source | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Server for SAP Applications 15 SP4 | kernel-syms | 0 | 5.14.21-150400.24.194.1 |
| SUSE:Linux Enterprise Workstation Extension 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.73.1 |
| SUSE:Real Time Module 15 SP6 | kernel-rt | 0 | 6.4.0-150600.10.55.1 |
| SUSE:Real Time Module 15 SP6 | kernel-rt_debug | 0 | 6.4.0-150600.10.55.1 |
| SUSE:Real Time Module 15 SP6 | kernel-source-rt | 0 | 6.4.0-150600.10.55.1 |
| SUSE:Real Time Module 15 SP6 | kernel-syms-rt | 0 | 6.4.0-150600.10.55.1 |
| SUSE:Real Time Module 15 SP7 | kernel-rt | 0 | 6.4.0-150700.7.19.1 |
| SUSE:Real Time Module 15 SP7 | kernel-source-rt | 0 | 6.4.0-150700.7.19.1 |
| SUSE:Real Time Module 15 SP7 | kernel-syms-rt | 0 | 6.4.0-150700.7.19.1 |
| openSUSE:Leap 15.6 | dtb-aarch64 | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-64kb | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-azure | 0 | 6.4.0-150600.8.52.1 |
| openSUSE:Leap 15.6 | kernel-debug | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-default | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-default-base | 0 | 6.4.0-150600.23.73.1.150600.12.32.1 |
| openSUSE:Leap 15.6 | kernel-docs | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-kvmsmall | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-obs-build | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-obs-qa | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-rt | 0 | 6.4.0-150600.10.55.1 |
| openSUSE:Leap 15.6 | kernel-rt_debug | 0 | 6.4.0-150600.10.55.1 |
| openSUSE:Leap 15.6 | kernel-source | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-source-azure | 0 | 6.4.0-150600.8.52.1 |
| openSUSE:Leap 15.6 | kernel-source-rt | 0 | 6.4.0-150600.10.55.1 |
| openSUSE:Leap 15.6 | kernel-syms | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 15.6 | kernel-syms-azure | 0 | 6.4.0-150600.8.52.1 |
| openSUSE:Leap 15.6 | kernel-syms-rt | 0 | 6.4.0-150600.10.55.1 |
| openSUSE:Leap 15.6 | kernel-zfcpdump | 0 | 6.4.0-150600.23.73.1 |
| openSUSE:Leap 16.0 | dtb-aarch64 | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-64kb | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-default | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-default-base | 0 | 6.12.0-160000.6.1.160000.2.4 |
| openSUSE:Leap 16.0 | kernel-docs | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-kvmsmall | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-obs-build | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-obs-qa | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-rt | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-source | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-syms | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-zfcpdump | 0 | 6.12.0-160000.6.1 |
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