| Release Date: | 2025-10-15 | |
| Impact: | Moderate | What is this? |
In the Linux kernel, the following vulnerability has been resolved:
nexthop: Forbid FDB status change while nexthop is in a group
The kernel forbids the creation of non-FDB nexthop groups with FDB
nexthops:
# ip nexthop add id 1 via 192.0.2.1 fdb
# ip nexthop add id 2 group 1
Error: Non FDB nexthop group cannot have fdb nexthops.
And vice versa:
# ip nexthop add id 3 via 192.0.2.2 dev dummy1
# ip nexthop add id 4 group 3 fdb
Error: FDB nexthop group can only have fdb nexthops.
However, as long as no routes are pointing to a non-FDB nexthop group,
the kernel allows changing the type of a nexthop from FDB to non-FDB and
vice versa:
# ip nexthop add id 5 via 192.0.2.2 dev dummy1
# ip nexthop add id 6 group 5
# ip nexthop replace id 5 via 192.0.2.2 fdb
# echo $?
0
This configuration is invalid and can result in a NPD [1] since FDB
nexthops are not associated with a nexthop device:
# ip route add 198.51.100.1/32 nhid 6
# ping 198.51.100.1
Fix by preventing nexthop FDB status change while the nexthop is in a
group:
# ip nexthop add id 7 via 192.0.2.2 dev dummy1
# ip nexthop add id 8 group 7
# ip nexthop replace id 7 via 192.0.2.2 fdb
Error: Cannot change nexthop FDB status while in a group.
[1]
BUG: kernel NULL pointer dereference, address: 00000000000003c0
[...]
Oops: Oops: 0000 [#1] SMP
CPU: 6 UID: 0 PID: 367 Comm: ping Not tainted 6.17.0-rc6-virtme-gb65678cacc03 #1 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014
RIP: 0010:fib_lookup_good_nhc+0x1e/0x80
[...]
Call Trace:
See more information about CVE-2025-39980 from MITRE CVE dictionary and NIST NVD
NOTE: The following CVSS metrics and score provided are preliminary and subject to review.
| Base Score: | 4.7 |
| Vector String: | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H |
| Version: | 3.1 |
| Attack Vector: | Local |
| Attack Complexity: | High |
| Privileges Required: | Low |
| User Interaction: | None |
| Scope: | Unchanged |
| Confidentiality Impact: | None |
| Integrity Impact: | None |
| Availability Impact: | High |
| Platform | Errata | Release Date |
| Oracle Linux version 8 (kernel-uek) | ELSA-2025-28048 | 2025-12-12 |
| Oracle Linux version 9 (kernel-uek) | ELSA-2025-28048 | 2025-12-12 |
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