Linux Kernel up to 6.3.2 fl_change initialization

Summaryinfo

A vulnerability identified as critical has been detected in Linux Kernel up to 6.3.2. Affected by this vulnerability is the function fl_change. The manipulation leads to initialization. This vulnerability is documented as CVE-2023-54206. There is not any exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.3.2. It has been rated as critical. This issue affects the function fl_change. The manipulation with an unknown input leads to a initialization vulnerability. Using CWE to declare the problem leads to CWE-665. The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used. The impact remains unknown. The summary by CVE is:

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---

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2023-54206 since 12/30/2025. The exploitation is known to be difficult. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 04/26/2026).

Upgrading to version 6.3.3 eliminates this vulnerability. Applying the patch 253a3a324e0ebc2825de76a0f5f17b8383b2023d/dd4f6bbfa646f258e5bcdfac57a5c413d687f588 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2025-2941). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Debian Linux
• Amazon Linux 2
• IBM Power Hardware Management Console
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• Open Source Linux Kernel
• RESF Rocky Linux
• IBM DataPower Gateway

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.3.0
• 6.3.1
• 6.3.2

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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