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CVE-2026-98023

Linux: vxlan: reject dynamic fdb entries that reference a nexthop id

Linux LinuxOperating systems
Open in ThreatlineRecord JSON
CVSS
7.8High
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.13%Chance of exploitation activity in the next 30 days, higher than 2% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in00c7f4b8144e535ffb931ad45942a1bd1315b882Also 55a33882808f1402052d53a08ead59aff8af18a1, 28f86eec851b7406a4bc6143f82aeba2882d9842 and 3 moreCVE List
Published25 Sep 2026Updated 19 Oct 2026CVE List

What fixes it

  • 00c7f4b8144e535ffb931ad45942a1bd1315b882LinuxCVE List
  • 55a33882808f1402052d53a08ead59aff8af18a1LinuxCVE List
  • 28f86eec851b7406a4bc6143f82aeba2882d9842LinuxCVE List
  • 53359916ceb649b7e6947c8c2f669368a41c1354LinuxCVE List
  • 3fa64d86fc64eda104e3e97721a12a42a2fd2073LinuxCVE List
  • 98fc57d167446b95b4e719815fe79edef93f8e7aLinuxCVE List

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Description

In the Linux kernel, the following vulnerability has been resolved:

vxlan: reject dynamic fdb entries that reference a nexthop id

The commit cited in the Fixes tag allowed VXLAN FDB entries to point to FDB nexthops so that overlay traffic could be load balanced across multiple VTEPs. Such entries can only be configured from user space, cannot be learned and cannot roam. They only make sense with a user space control plane such as E-VPN where data plane learning is disabled.

Despite that, the VXLAN driver does not currently prevent such entries from being configured with the "dynamic" flag. The per-nexthop FDB list is only protected by the per-device hash lock, which is not sufficient when two VXLAN devices point to the same FDB nexthop and therefore share the list. Aging runs in softirq context without RTNL, so an entry deleted by one device can race with an addition or deletion from the other, leading to list corruption:

list_del corruption. next->prev should be ffff8881069d9548, but was dead000000000122. (next=ffff8881069d9448) WARNING: CPU: 0 PID: 90 at lib/list_debug.c:65 __list_del_entry_valid_or_report+0x1aa/0x210 ... vxlan_fdb_destroy+0x5b8/0xad0 vxlan_cleanup+0x328/0x450 call_timer_fn+0x2a/0x1c0 run_timer_softirq+0x18c/0x210 BUG: KASAN: slab-use-after-free in vxlan_fdb_destroy

Fix this by rejecting the bogus configuration of dynamic FDB entries that point to FDB nexthops, both when created and when an existing entry is updated. As such, the per-nexthop FDB list is only ever mutated under the RTNL lock. Add test cases to make sure that this does not regress in the future.

Text from CVE List

Affected versions 18

  • Linuxaffected: 1274e1cc42264d4e629841e4f182795cb0becfd2 before 00c7f4b8144e535ffb931ad45942a1bd1315b882CVE List
  • Linuxaffected: 1274e1cc42264d4e629841e4f182795cb0becfd2 before 55a33882808f1402052d53a08ead59aff8af18a1CVE List
  • Linuxaffected: 1274e1cc42264d4e629841e4f182795cb0becfd2 before c8f29af91e0830fdabc9aa1eb1a0f898ce1bc603CVE List
  • Linuxaffected: 1274e1cc42264d4e629841e4f182795cb0becfd2 before b2a8e165ddb6cd72176890b2954c52b0f6dbce1aCVE List
  • Linuxaffected: 1274e1cc42264d4e629841e4f182795cb0becfd2 before 28f86eec851b7406a4bc6143f82aeba2882d9842CVE List
  • Linuxaffected: 1274e1cc42264d4e629841e4f182795cb0becfd2 before 53359916ceb649b7e6947c8c2f669368a41c1354CVE List
  • Linuxaffected: 1274e1cc42264d4e629841e4f182795cb0becfd2 before 3fa64d86fc64eda104e3e97721a12a42a2fd2073CVE List
  • Linuxaffected: 1274e1cc42264d4e629841e4f182795cb0becfd2 before 98fc57d167446b95b4e719815fe79edef93f8e7aCVE List
  • Linuxaffected: 5.8CVE List
  • Linuxunaffected: all versions before 5.8CVE List
  • Linuxunaffected: 5.10.271 through 5.10.*CVE List
  • Linuxunaffected: 5.15.222 through 5.15.*CVE List
  • Linuxunaffected: 6.1.189 through 6.1.*CVE List
  • Linuxunaffected: 6.6.158 through 6.6.*CVE List
  • Linuxunaffected: 6.12.111 through 6.12.*CVE List
  • Linuxunaffected: 6.18.53 through 6.18.*CVE List
  • Linuxunaffected: 7.2.7 through 7.2.*CVE List
  • Linuxunaffected: 7.3CVE List

References 8