{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-39894", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2025-04-16T07:20:57.145Z", "datePublished": "2025-10-01T07:42:43.126Z", "dateUpdated": "2026-08-05T12:05:56.359Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:05:56.359Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after confirm\n\nWhen send a broadcast packet to a tap device, which was added to a bridge,\nbr_nf_local_in() is called to confirm the conntrack. If another conntrack\nwith the same hash value is added to the hash table, which can be\ntriggered by a normal packet to a non-bridge device, the below warning\nmay happen.\n\n ------------[ cut here ]------------\n WARNING: CPU: 1 PID: 96 at net/bridge/br_netfilter_hooks.c:632 br_nf_local_in+0x168/0x200\n CPU: 1 UID: 0 PID: 96 Comm: tap_send Not tainted 6.17.0-rc2-dirty #44 PREEMPT(voluntary)\n RIP: 0010:br_nf_local_in+0x168/0x200\n Call Trace:\n \n nf_hook_slow+0x3e/0xf0\n br_pass_frame_up+0x103/0x180\n br_handle_frame_finish+0x2de/0x5b0\n br_nf_hook_thresh+0xc0/0x120\n br_nf_pre_routing_finish+0x168/0x3a0\n br_nf_pre_routing+0x237/0x5e0\n br_handle_frame+0x1ec/0x3c0\n __netif_receive_skb_core+0x225/0x1210\n __netif_receive_skb_one_core+0x37/0xa0\n netif_receive_skb+0x36/0x160\n tun_get_user+0xa54/0x10c0\n tun_chr_write_iter+0x65/0xb0\n vfs_write+0x305/0x410\n ksys_write+0x60/0xd0\n do_syscall_64+0xa4/0x260\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\n \n ---[ end trace 0000000000000000 ]---\n\nTo solve the hash conflict, nf_ct_resolve_clash() try to merge the\nconntracks, and update skb->_nfct. However, br_nf_local_in() still use the\nold ct from local variable 'nfct' after confirm(), which leads to this\nwarning.\n\nIf confirm() does not insert the conntrack entry and return NF_DROP, the\nwarning may also occur. There is no need to reserve the WARN_ON_ONCE, just\nremove it." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:N - The trigger is a broadcast/multicast IP frame arriving on a bridge port and being locally delivered via br_pass_frame_up() → NF_BR_LOCAL_IN, requiring no host access at all; on the very common overlay deployments (VXLAN/GRE port enslaved to a Linux bridge in Docker overlay, k8s CNI, OpenStack) those inner broadcast frames originate from a routed, remote VTEP, making the vulnerable code reachable across layer 3.\nAC:L - The attacker drives both sides of the clash by flooding duplicate same-tuple broadcast datagrams, which the bridge itself fans out concurrently (flood to N ports plus local receive, plus a copy to a non-bridge device as noted in the commit), so two unconfirmed conntracks with an identical tuple reach __nf_conntrack_confirm() in parallel. The required br_netfilter+conntrack+bridge configuration is the default on container and virtualization hosts, not a rare option.\nPR:N - No credentials or capabilities on the target are needed — the attacker only has to get an IP broadcast/multicast frame onto a segment bridged by the victim, which is unauthenticated packet delivery.\nUI:N - No victim action is required; the bridge processes the received frames automatically in softirq context.\nS:U - The stale conntrack read and the WARNING both occur in the host kernel's own netfilter/bridge context, with no crossing of a VM, IOMMU, or sandbox boundary.\nC:N - The stale read is a single unsigned long from a SLAB_TYPESAFE_BY_RCU nf_conn object and its value is consumed only by the WARN condition — it is never returned to the attacker, and the remote attacker has no channel to read the resulting dmesg splat.\nI:N - No write occurs on the stale pointer; confirm() has already repointed skb->_nfct at the surviving conntrack with a valid reference, so no kernel memory is modified and no control flow is influenced.\nA:H - The bug fires a kernel WARNING from a remotely reachable softirq path, which taints the kernel and causes an immediate panic on the many hardened, Android, ChromeOS, and cloud/CI deployments that run with panic_on_warn=1, yielding a full denial of service." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/bridge/br_netfilter_hooks.c" ], "versions": [ { "version": "7c3f28599652acf431a2211168de4a583f30b6d5", "lessThan": "d00c8b0daf56012f69075e3377da67878c775e4c", "status": "affected", "versionType": "git" }, { "version": "2b1414d5e94e477edff1d2c79030f1d742625ea0", "lessThan": "ccbad4803225eafe0175d3cb19f0d8d73b504a94", "status": "affected", "versionType": "git" }, { "version": "80cd0487f630b5382734997c3e5e3003a77db315", "lessThan": "50db11e2bbb635e38e3dd096215580d6adb41fb0", "status": "affected", "versionType": "git" }, { "version": "62e7151ae3eb465e0ab52a20c941ff33bb6332e9", "lessThan": "c47ca77fee9071aa543bae592dd2a384f895c8b6", "status": "affected", "versionType": "git" }, { "version": "62e7151ae3eb465e0ab52a20c941ff33bb6332e9", "lessThan": "a74abcf0f09f59daeecf7a3ba9c1d690808b0afe", "status": "affected", "versionType": "git" }, { "version": "62e7151ae3eb465e0ab52a20c941ff33bb6332e9", "lessThan": "479a54ab92087318514c82428a87af2d7af1a576", "status": "affected", "versionType": "git" }, { "version": "cb734975b0ffa688ff6cc0eed463865bf07b6c01", "status": "affected", "versionType": "git" }, { "version": "5.15.151", "lessThan": "5.15.192", "status": "affected", "versionType": "semver" }, { "version": "6.1.81", "lessThan": "6.1.151", "status": "affected", "versionType": "semver" }, { "version": "6.6.21", "lessThan": "6.6.105", "status": "affected", "versionType": "semver" }, { "version": "6.7.9", "lessThan": "6.8", "status": "affected", "versionType": "semver" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/bridge/br_netfilter_hooks.c" ], "versions": [ { "version": "6.8", "status": "affected" }, { "version": "0", "lessThan": "6.8", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.192", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.151", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.105", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.46", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.16.6", "lessThanOrEqual": "6.16.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.17", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15.151", "versionEndExcluding": "5.15.192" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.1.81", "versionEndExcluding": "6.1.151" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6.21", "versionEndExcluding": "6.6.105" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.8", "versionEndExcluding": "6.12.46" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.8", "versionEndExcluding": "6.16.6" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.8", "versionEndExcluding": "6.17" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7.9" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/d00c8b0daf56012f69075e3377da67878c775e4c" }, { "url": "https://git.kernel.org/stable/c/ccbad4803225eafe0175d3cb19f0d8d73b504a94" }, { "url": "https://git.kernel.org/stable/c/50db11e2bbb635e38e3dd096215580d6adb41fb0" }, { "url": "https://git.kernel.org/stable/c/c47ca77fee9071aa543bae592dd2a384f895c8b6" }, { "url": "https://git.kernel.org/stable/c/a74abcf0f09f59daeecf7a3ba9c1d690808b0afe" }, { "url": "https://git.kernel.org/stable/c/479a54ab92087318514c82428a87af2d7af1a576" } ], "title": "netfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after confirm", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "title": "CVE Program Container", "references": [ { "url": "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html" } ], "providerMetadata": { "orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2025-11-03T17:44:28.733Z" } } ] } }