{"id":"AZL-68507","summary":"CVE-2025-39980 affecting package kernel for versions less than 6.6.112.1-1","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnexthop: Forbid FDB status change while nexthop is in a group\n\nThe kernel forbids the creation of non-FDB nexthop groups with FDB\nnexthops:\n\n # ip nexthop add id 1 via 192.0.2.1 fdb\n # ip nexthop add id 2 group 1\n Error: Non FDB nexthop group cannot have fdb nexthops.\n\nAnd vice versa:\n\n # ip nexthop add id 3 via 192.0.2.2 dev dummy1\n # ip nexthop add id 4 group 3 fdb\n Error: FDB nexthop group can only have fdb nexthops.\n\nHowever, as long as no routes are pointing to a non-FDB nexthop group,\nthe kernel allows changing the type of a nexthop from FDB to non-FDB and\nvice versa:\n\n # ip nexthop add id 5 via 192.0.2.2 dev dummy1\n # ip nexthop add id 6 group 5\n # ip nexthop replace id 5 via 192.0.2.2 fdb\n # echo $?\n 0\n\nThis configuration is invalid and can result in a NPD [1] since FDB\nnexthops are not associated with a nexthop device:\n\n # ip route add 198.51.100.1/32 nhid 6\n # ping 198.51.100.1\n\nFix by preventing nexthop FDB status change while the nexthop is in a\ngroup:\n\n # ip nexthop add id 7 via 192.0.2.2 dev dummy1\n # ip nexthop add id 8 group 7\n # ip nexthop replace id 7 via 192.0.2.2 fdb\n Error: Cannot change nexthop FDB status while in a group.\n\n[1]\nBUG: kernel NULL pointer dereference, address: 00000000000003c0\n[...]\nOops: Oops: 0000 [#1] SMP\nCPU: 6 UID: 0 PID: 367 Comm: ping Not tainted 6.17.0-rc6-virtme-gb65678cacc03 #1 PREEMPT(voluntary)\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014\nRIP: 0010:fib_lookup_good_nhc+0x1e/0x80\n[...]\nCall Trace:\n \u003cTASK\u003e\n fib_table_lookup+0x541/0x650\n ip_route_output_key_hash_rcu+0x2ea/0x970\n ip_route_output_key_hash+0x55/0x80\n __ip4_datagram_connect+0x250/0x330\n udp_connect+0x2b/0x60\n __sys_connect+0x9c/0xd0\n __x64_sys_connect+0x18/0x20\n do_syscall_64+0xa4/0x2a0\n entry_SYSCALL_64_after_hwframe+0x4b/0x53","modified":"2026-04-21T04:38:26.609604Z","published":"2025-10-15T08:15:35Z","upstream":["CVE-2025-39980"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-39980"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6.112.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-68507.json"}}],"schema_version":"1.7.5"}