# CVE-2025-39980

## Summary

- **CVE ID:** CVE-2025-39980
- **Severity:** UNKNOWN
- **CVSS Score:** 1.51
- **CWE:** N/A
- **Published:** Oct 15, 2025
- **Last Modified:** Sep 17, 2026

## Description

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:
 <TASK>
 fib_table_lookup+0x541/0x650
 ip_route_output_key_hash_rcu+0x2ea/0x970
 ip_route_output_key_hash+0x55/0x80
 __ip4_datagram_connect+0x250/0x330
 udp_connect+0x2b/0x60
 __sys_connect+0x9c/0xd0
 __x64_sys_connect+0x18/0x20
 do_syscall_64+0xa4/0x2a0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

## Affected Products

- Linux — Linux (38428d68719c454d269cb03b776d8a4b0ad66111)
- Linux — Linux (5.8)
- Linux — Linux (0)
- Linux — Linux (5.10.245)
- Linux — Linux (5.15.194)
- Linux — Linux (6.1.155)
- Linux — Linux (6.6.109)
- Linux — Linux (6.12.50)
- Linux — Linux (6.16.10)
- Linux — Linux (6.17)

## References

- [CNA](https://git.kernel.org/stable/c/e1e87ac0daacd51f522ecd1645cd76b5809303ed)
- [CNA](https://git.kernel.org/stable/c/0e7bfe7a268ccbd7859730c529161cafbf44637c)
- [CNA](https://git.kernel.org/stable/c/ec428fff792b7bd15b248dafca2e654b666b1304)
- [CNA](https://git.kernel.org/stable/c/24046d31f6f92220852d393d510b6062843e3fbd)
- [CNA](https://git.kernel.org/stable/c/f0e49fd13afe9dea7a09a1c9537fd00cea22badb)
- [CNA](https://git.kernel.org/stable/c/8dd4aa0122885f710930de135af2adc4ccc3238f)
- [CNA](https://git.kernel.org/stable/c/390b3a300d7872cef9588f003b204398be69ce08)
- [siemens-SADP](https://cert-portal.siemens.com/productcert/html/ssa-019113.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.21%
- **EPSS Percentile:** 11.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._