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:

__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

Classification

CVE ID: CVE-2025-37921

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 11.93% (scored less or equal to compared to others)

EPSS Date: 2025-06-18 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-37921
https://git.kernel.org/stable/c/2d4a121296aa3940d2df9906f955c2b6b4e38bc3
https://git.kernel.org/stable/c/3576e9a80b6c4381b01ce0cbaa07f5e92d4492ed
https://git.kernel.org/stable/c/5cb9e07f84e527974b12e82e2549fa6c0cc6eef0
https://git.kernel.org/stable/c/470206205588559e60035fceb5f256640cb45f99
https://git.kernel.org/stable/c/087a9eb9e5978e3ba362e1163691e41097e8ca20

Timeline