# CVE-2023-54206: net/sched: flower: fix filter idr initialization

> A race condition in the Linux kernel flower classifier allows concurrent access to uninitialized filters, causing a NULL pointer dereference and system crash.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 30 Dec 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2023-54206, GHSA-v2jm-777x-22hp, UBUNTU-CVE-2023-54206

## What is CVE-2023-54206?

CVE-2023-54206 is a high-severity vulnerability in Linux, published on 30 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: flower: fix filter idr initialization

The cited commit moved idr initialization too early in fl_change() which
allows concurrent users to access the filter that is still being
initialized and is in inconsistent state, which, in turn, can cause NULL
pointer dereference [0]. Since there is no obvious way to fix the ordering
without reverting the whole cited commit, alternative approach taken to
first insert NULL pointer into idr in order to allocate the handle but
still cause fl_get() to return NULL and prevent concurrent users from
seeing the filter while providing miss-to-action infrastructure with valid
handle id early in fl_change().

[  152.434728] general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN
[  152.436163] KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
[  152.437269] CPU: 4 PID: 3877 Comm: tc Not tainted 6.3.0-rc4+ #5
[  152.438110] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[  152.439644] RIP: 0010:fl_dump_key+0x8b/0x1d10 [cls_flower]
[  152.440461] Code: 01 f2 02 f2 c7 40 08 04 f2 04 f2 c7 40 0c 04 f3 f3 f3 65 48 8b 04 25 28 00 00 00 48 89 84 24 00 01 00 00 48 89 c8 48 c1 e8 03 <0f> b6 04 10 84 c0 74 08 3c 03 0f 8e 98 19 00 00 8b 13 85 d2 74 57
[  152.442885] RSP: 0018:ffff88817a28f158 EFLAGS: 00010246
[  152.443851] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[  152.444826] RDX: dffffc0000000000 RSI: ffffffff8500ae80 RDI: ffff88810a987900
[  152.445791] RBP: ffff888179d88240 R08: ffff888179d8845c R09: ffff888179d88240
[  152.446780] R10: ffffed102f451e48 R11: 00000000fffffff2 R12: ffff88810a987900
[  152.447741] R13: ffffffff8500ae80 R14: ffff88810a987900 R15: ffff888149b3c738
[  152.448756] FS:  00007f5eb2a34800(0000) GS:ffff88881ec00000(0000) knlGS:0000000000000000
[  152.449888] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  152.450685] CR2: 000000000046ad19 CR3: 000000010b0bd006 CR4: 0000000000370ea0
[  152.451641] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  152.452628] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  152.453588] Call Trace:
[  152.454032]  <TASK>
[  152.454447]  ? netlink_sendmsg+0x7a1/0xcb0
[  152.455109]  ? sock_sendmsg+0xc5/0x190
[  152.455689]  ? ____sys_sendmsg+0x535/0x6b0
[  152.456320]  ? ___sys_sendmsg+0xeb/0x170
[  152.456916]  ? do_syscall_64+0x3d/0x90
[  152.457529]  ? entry_SYSCALL_64_after_hwframe+0x46/0xb0
[  152.458321]  ? ___sys_sendmsg+0xeb/0x170
[  152.458958]  ? __sys_sendmsg+0xb5/0x140
[  152.459564]  ? do_syscall_64+0x3d/0x90
[  152.460122]  ? entry_SYSCALL_64_after_hwframe+0x46/0xb0
[  152.460852]  ? fl_dump_key_options.part.0+0xea0/0xea0 [cls_flower]
[  152.461710]  ? _raw_spin_lock+0x7a/0xd0
[  152.462299]  ? _raw_read_lock_irq+0x30/0x30
[  152.462924]  ? nla_put+0x15e/0x1c0
[  152.463480]  fl_dump+0x228/0x650 [cls_flower]
[  152.464112]  ? fl_tmplt_dump+0x210/0x210 [cls_flower]
[  152.464854]  ? __kmem_cache_alloc_node+0x1a7/0x330
[  152.465592]  ? nla_put+0x15e/0x1c0
[  152.466160]  tcf_fill_node+0x515/0x9a0
[  152.466766]  ? tc_setup_offload_action+0xf0/0xf0
[  152.467463]  ? __alloc_skb+0x13c/0x2a0
[  152.468067]  ? __build_skb_around+0x330/0x330
[  152.468814]  ? fl_get+0x107/0x1a0 [cls_flower]
[  152.469503]  tc_del_tfilter+0x718/0x1330
[  152.470115]  ? is_bpf_text_address+0xa/0x20
[  152.470765]  ? tc_ctl_chain+0xee0/0xee0
[  152.471335]  ? __kernel_text_address+0xe/0x30
[  152.471948]  ? unwind_get_return_address+0x56/0xa0
[  152.472639]  ? __thaw_task+0x150/0x150
[  152.473218]  ? arch_stack_walk+0x98/0xf0
[  152.473839]  ? __stack_depot_save+0x35/0x4c0
[  152.474501]  ? stack_trace_save+0x91/0xc0
[  152.475119]  ? security_capable+0x51/0x90
[  152.475741]  rtnetlink_rcv_msg+0x2c1/0x9d0
[  152.476387]  ? rtnl_calcit.isra.0+0x2b0/0x2b0
[  152.477042]
---truncated---

## Which versions are affected by CVE-2023-54206?


## How do I fix CVE-2023-54206?

Apply the vendor's patch.

## Is CVE-2023-54206 being exploited?

There is no known exploitation of CVE-2023-54206 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-54206 and fix it if it is affected.

What it is: CVE-2023-54206 is a high-severity vulnerability in Linux, published on 30 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-54206 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-54206/ (Markdown: https://insights.sbomify.com/CVE-2023-54206/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-54206
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-54206
- OSV: https://osv.dev/vulnerability/CVE-2023-54206

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-54206/
Summaries are generated and may contain mistakes; the official description above is the record.