CVE-2025-39894High· 7.5▾ TwilightIn 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_…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0.1 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake. The CVSS score shown above comes from the assigning CNA record, not NVD.
Exploit-prediction probability, daily snapshots since Oct 15.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
Last analysed / modified upstream
0.3%
0.3% → 0.3%
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.
Linux >= 7c3f28599652acf431a2211168de4a583f30b6d5 < d00c8b0daf56012f69075e3377da67878c775e4cLinux >= 2b1414d5e94e477edff1d2c79030f1d742625ea0 < ccbad4803225eafe0175d3cb19f0d8d73b504a94Linux >= 80cd0487f630b5382734997c3e5e3003a77db315 < 50db11e2bbb635e38e3dd096215580d6adb41fb0Linux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 < c47ca77fee9071aa543bae592dd2a384f895c8b6Linux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 < a74abcf0f09f59daeecf7a3ba9c1d690808b0afeLinux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 < 479a54ab92087318514c82428a87af2d7af1a576Linux cb734975b0ffa688ff6cc0eed463865bf07b6c01Linux >= 5.15.151 < 5.15.192Linux >= 6.1.81 < 6.1.151Linux >= 6.6.21 < 6.6.105Linux >= 6.7.9 < 6.8Linux 6.8Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
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