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CVE-2025-39851— vxlan: Fix NPD when refreshing an FDB entry with a nexthop object

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于未正确处理指向FDB nexthop组的FDB条目，可能导致空指针取消引用。

CVSS 7.5 · High EPSS 0.30% · P21

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 10

VendorProduct Version RangeStatus
Linux Linux 1274e1cc42264d4e629841e4f182795cb0becfd2< 18e4b315e359fa0505eee318a0cb745240122e2f affected
1274e1cc42264d4e629841e4f182795cb0becfd2< 4ff4f3104da6507e0f118c63c4560dfdeb59dce3 affected
1274e1cc42264d4e629841e4f182795cb0becfd2< 0e8630f24c14d9c655d19eabe2e52a9e9f713307 affected
1274e1cc42264d4e629841e4f182795cb0becfd2< 6ead38147ebb813f08be6ea8ef547a0e4c09559a affected
5.8 affected
< 5.8 unaffected
6.6.160≤ 6.6.* unaffected
6.12.46≤ 6.12.* unaffected
… +2 more rows
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I. Basic Information for CVE-2025-39851

Vulnerability Information
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Vulnerability Title
vxlan: Fix NPD when refreshing an FDB entry with a nexthop object
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: vxlan: Fix NPD when refreshing an FDB entry with a nexthop object VXLAN FDB entries can point to either a remote destination or an FDB nexthop group. The latter is usually used in EVPN deployments where learning is disabled. However, when learning is enabled, an incoming packet might try to refresh an FDB entry that points to an FDB nexthop group and therefore does not have a remote. Such packets should be dropped, but they are only dropped after dereferencing the non-existent remote, resulting in a NPD [1] which can be reproduced using [2]. Fix by dropping such packets earlier. Remove the misleading comment from first_remote_rcu(). [1] BUG: kernel NULL pointer dereference, address: 0000000000000000 [...] CPU: 13 UID: 0 PID: 361 Comm: mausezahn Not tainted 6.17.0-rc1-virtme-g9f6b606b6b37 #1 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014 RIP: 0010:vxlan_snoop+0x98/0x1e0 [...] Call Trace: <TASK> vxlan_encap_bypass+0x209/0x240 encap_bypass_if_local+0xb1/0x100 vxlan_xmit_one+0x1375/0x17e0 vxlan_xmit+0x6b4/0x15f0 dev_hard_start_xmit+0x5d/0x1c0 __dev_queue_xmit+0x246/0xfd0 packet_sendmsg+0x113a/0x1850 __sock_sendmsg+0x38/0x70 __sys_sendto+0x126/0x180 __x64_sys_sendto+0x24/0x30 do_syscall_64+0xa4/0x260 entry_SYSCALL_64_after_hwframe+0x4b/0x53 [2] #!/bin/bash ip address add 192.0.2.1/32 dev lo ip address add 192.0.2.2/32 dev lo ip nexthop add id 1 via 192.0.2.3 fdb ip nexthop add id 10 group 1 fdb ip link add name vx0 up type vxlan id 10010 local 192.0.2.1 dstport 12345 localbypass ip link add name vx1 up type vxlan id 10020 local 192.0.2.2 dstport 54321 learning bridge fdb add 00:11:22:33:44:55 dev vx0 self static dst 192.0.2.2 port 54321 vni 10020 bridge fdb add 00:aa:bb:cc:dd:ee dev vx1 self static nhid 10 mausezahn vx0 -a 00:aa:bb:cc:dd:ee -b 00:11:22:33:44:55 -c 1 -q
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于未正确处理指向FDB nexthop组的FDB条目，可能导致空指针取消引用。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 1274e1cc42264d4e629841e4f182795cb0becfd2 ~ 18e4b315e359fa0505eee318a0cb745240122e2f -
Linux Linux 5.8 -

II. Public POCs for CVE-2025-39851

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III. Intelligence Information for CVE-2025-39851

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Patches & Fixes for CVE-2025-39851 (1)

Same Patch Batch · Linux · 2025-09-19 · 30 CVEs total

CVE-2025-39841 9.8 CRITICAL scsi: lpfc: Fix buffer free/clear order in deferred receive path
CVE-2025-39864 8.8 HIGH wifi: cfg80211: fix use-after-free in cmp_bss()
CVE-2025-39862 8.8 HIGH wifi: mt76: mt7915: fix list corruption after hardware restart
CVE-2025-39848 8.8 HIGH ax25: properly unshare skbs in ax25_kiss_rcv()
CVE-2025-39839 8.8 HIGH batman-adv: fix OOB read/write in network-coding decode
CVE-2025-39849 8.8 HIGH wifi: cfg80211: sme: cap SSID length in __cfg80211_connect_result()
CVE-2025-39860 8.0 HIGH Bluetooth: Fix use-after-free in l2cap_sock_cleanup_listen()
CVE-2025-39837 7.8 HIGH platform/x86: asus-wmi: Fix racy registrations
CVE-2025-39863 7.8 HIGH wifi: brcmfmac: fix use-after-free when rescheduling brcmf_btcoex_info work
CVE-2025-39866 7.8 HIGH fs: writeback: fix use-after-free in __mark_inode_dirty()
CVE-2025-39854 7.8 HIGH ice: fix NULL access of tx->in_use in ice_ll_ts_intr
CVE-2025-39857 7.5 HIGH net/smc: fix one NULL pointer dereference in smc_ib_is_sg_need_sync()
CVE-2025-39840 7.1 HIGH audit: fix out-of-bounds read in audit_compare_dname_path()
CVE-2025-39842 ocfs2: prevent release journal inode after journal shutdown
CVE-2025-39844 mm: move page table sync declarations to linux/pgtable.h
CVE-2025-39852 net/tcp: Fix socket memory leak in TCP-AO failure handling for IPv6
CVE-2025-39843 mm: slub: avoid wake up kswapd in set_track_prepare
CVE-2025-39838 cifs: prevent NULL pointer dereference in UTF16 conversion
CVE-2025-39845 x86/mm/64: define ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings()
CVE-2025-39846 pcmcia: Fix a NULL pointer dereference in __iodyn_find_io_region()

Showing top 20 of 30 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2025-39851

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