CVE-2025-37921 vxlan: vnifilter: Fix unlocked deletion of default FDB entry
A race condition in the Linux kernel VXLAN driver allows local attackers to trigger a kernel warning and potential denial of service by deleting VNI filters without proper locking.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-37921?
CVE-2025-37921 is a high-severity vulnerability in Debian Debian Linux, published on 20 May 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
vxlan: vnifilter: Fix unlocked deletion of default FDB entry
When a VNI is deleted from a VXLAN device in 'vnifilter' mode, the FDB entry associated with the default remote (assuming one was configured) is deleted without holding the hash lock. This is wrong and will result in a warning [1] being generated by the lockdep annotation that was added by commit ebe642067455 ("vxlan: Create wrappers for FDB lookup").
Reproducer:
# ip link add vx0 up type vxlan dstport 4789 external vnifilter local 192.0.2.1 # bridge vni add vni 10010 remote 198.51.100.1 dev vx0 # bridge vni del vni 10010 dev vx0
Fix by acquiring the hash lock before the deletion and releasing it afterwards. Blame the original commit that introduced the issue rather than the one that exposed it.
[1] WARNING: CPU: 3 PID: 392 at drivers/net/vxlan/vxlan_core.c:417 vxlan_find_mac+0x17f/0x1a0 [...] RIP: 0010:vxlan_find_mac+0x17f/0x1a0 [...] Call Trace: <TASK> __vxlan_fdb_delete+0xbe/0x560 vxlan_vni_delete_group+0x2ba/0x940 vxlan_vni_del.isra.0+0x15f/0x580 vxlan_process_vni_filter+0x38b/0x7b0 vxlan_vnifilter_process+0x3bb/0x510 rtnetlink_rcv_msg+0x2f7/0xb70 netlink_rcv_skb+0x131/0x360 netlink_unicast+0x426/0x710 netlink_sendmsg+0x75a/0xc20 __sock_sendmsg+0xc1/0x150 ____sys_sendmsg+0x5aa/0x7b0 ___sys_sendmsg+0xfc/0x180 __sys_sendmsg+0x121/0x1b0 do_syscall_64+0xbb/0x1d0 entry_SYSCALL_64_after_hwframe+0x4b/0x53
Which versions are affected by CVE-2025-37921?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-37921?
Apply the vendor's patch.
Is CVE-2025-37921 being exploited?
There is no known exploitation of CVE-2025-37921 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as BELL-CVE-2025-37921, DEBIAN-CVE-2025-37921, GHSA-x58j-hw5g-jqcq, ROOT-OS-DEBIAN-12-CVE-2025-37921, ROOT-OS-UBUNTU-2404-CVE-2025-37921, UBUNTU-CVE-2025-37921.